Multi-layer dispersion-engineered waveguides and resonators

ABSTRACT

A multi-layer laterally-confined dispersion-engineered optical waveguide may include one multi-layer reflector stack for guiding an optical mode along a surface thereof, or may include two multi-layer reflector stacks with a core therebetween for guiding an optical mode along the core. Dispersive properties of such multi-layer waveguides enable modal-index-matching between low-index optical fibers and/or waveguides and high-index integrated optical components and efficient transfer of optical signal power therebetween. Integrated optical devices incorporating such multi-layer waveguides may therefore exhibit low (&lt;3 dB) insertion losses. Incorporation of an active layer (electro-optic, electro-absorptive, non-linear-optical) into such waveguides enables active control of optical loss and/or modal index with relatively low-voltage/low-intensity control signals. Integrated optical devices incorporating such waveguides may therefore exhibit relatively low drive signal requirements.

RELATED APPLICATIONS

[0001] This application claims priority based on prior-filed co-pendingU.S. provisional Application No. 60/257,218 entitled “Waveguides andresonators for integrated optical devices and methods of fabrication anduse thereof”, filed Dec. 21, 2000 in the name of Oskar J. Painter, saidprovisional application being hereby incorporated by reference in itsentirety as if fully set forth herein. This application claims prioritybased on prior-filed co-pending U.S. provisional Application No.60/257,248 entitled “Modulators for resonant optical power controldevices and methods of fabrication and use thereof”, filed Dec. 21, 2000in the names of Oskar J. Painter, Kerry J. Vahala, Peter C. Sercel, andGuido Hunziker, said provisional application being hereby incorporatedby reference in its entirety as if fully set forth herein. Thisapplication claims priority based on prior-filed co-pending U.S.provisional Application No. 60/301,519 entitled “Waveguide-fiberMach-Zender interferometer and methods of fabrication and use thereof”,filed Jun. 27, 2001 in the names of Oskar J. Painter, David W. Vernooy,and Kerry J. Vahala, said provisional application being herebyincorporated by reference in its entirety as if fully set forth herein.

GOVERNMENT RIGHTS

[0002] The U.S. Government may have limited rights in this applicationpursuant to DARPA Contract No. N00014-00-3-0023.

FIELD OF THE INVENTION

[0003] The field of the present invention relates to devices formodulating, routing and/or processing optical signal power transmission.In particular, optical waveguides and resonators for integrated opticaldevices, as well as methods of fabrication and use thereof, aredisclosed herein. The waveguides and resonators include a multi-layerlaterally-confined dispersion-engineered waveguide segment, and mayfurther include one or more active layers, thereby enabling tailoring ofoptical properties of the waveguide/resonator, and/or controlledmodulation thereof.

BACKGROUND

[0004] This application is related to subject matter disclosed in:

[0005] A1) U.S. provisional Application No. 60/111,484 entitled “Anall-fiber-optic modulator” filed Dec. 7, 1998 in the names of Kerry J.Vahala and Amnon Yariv, said provisional application being herebyincorporated by reference in its entirety as if fully set forth herein;

[0006] A2) U.S. application No. 09/454,719 entitled “Resonant opticalwave power control devices and methods” filed Dec. 7, 1999 in the namesof Kerry J. Vahala and Amnon Yariv, said application being herebyincorporated by reference in its entirety as if fully set forth herein;

[0007] A3) U.S. provisional Application No. 60/108,358 entitled “Dualtapered fiber-microsphere coupler” filed Nov. 13, 1998 in the names ofKerry J. Vahala and Ming Cai, said provisional application being herebyincorporated by reference in its entirety as if fully set forth herein;

[0008] A4) U.S. application No. 09/440,311 entitled “Resonator fiberbi-directional coupler” filed Nov. 12, 1999 in the names of Kerry J.Vahala, Ming Cai, and Guido Hunziker, said application being herebyincorporated by reference in its entirety as if fully set forth herein;

[0009] A5) U.S. provisional Application No.60/183,499 entitled “Resonantoptical power control devices and methods of fabrication thereof” filedFeb. 17, 2000 in the names of Peter C. Sercel and Kerry J. Vahala, saidprovisional application being hereby incorporated by reference in itsentirety as if fully set forth herein;

[0010] A6) U.S. provisional Application No.60/226,147 entitled“Fiber-optic waveguides for evanescent optical coupling and methods offabrication and use thereof”, filed Aug. 18, 2000 in the names of PeterC. Sercel, Guido Hunziker, and Robert B. Lee, said provisionalapplication being hereby incorporated by reference in its entirety as iffully set forth herein;

[0011] A7) U.S. provisional Application No. 60/170,074 entitled “Opticalrouting/switching based on control of waveguide-ring resonatorcoupling”, filed Dec. 9, 1999 in the name of Amnon a Yariv, saidprovisional application being hereby incorporated by reference in itsentirety as if fully set forth herein;

[0012] A8) U.S. Pat. No.6,052,495 entitled “Resonator modulators andwavelength routing switches” issued Apr. 18, 2000 in the names of BrentE. Little, James S. Foresi, and Hermann A. Haus, said patent beinghereby incorporated by reference in its entirety as if fully set forthherein;

[0013] A9) U. S. Pat. No.6,101,300 entitled “High efficiency channeldrop filter with absorption induced on/off switching and modulation”issued Aug. 8, 2000 in the names of Shanhui Fan, Pierre R. Villeneuve,John D. Joannopoulos, Brent E. Little, and Hermann A. Haus, said patentbeing hereby incorporated by reference in its entirety as if fully setforth herein;

[0014] A10) U. S. Pat. No. 5,926,496 entitled “Semiconductormicro-resonator device” issued Jul. 20, 1999 in the names of Seng-TiongHo and Deanna Rafizadeh, said patent being hereby incorporated byreference in its entirety as if fully set forth herein; and

[0015] A11) U. S. Pat. No. 6,009,115 entitled “Semiconductormicro-resonator device” issued Dec. 28, 1999 in the name of Seng-TiongHo, said patent being hereby incorporated by reference in its entiretyas if fully set forth herein.

[0016] A12) U.S. provisional Application No.60/257,218 entitled“Waveguides and resonators for integrated optical devices and methods offabrication and use thereof”, filed Dec. 21, 2000 in the name of OskarJ. Painter, said provisional application being hereby incorporated byreference in its entirety as if fully set forth herein;

[0017] A13) U.S. provisional Application No.60/257,248 entitled“Modulators for resonant optical power control devices and methods offabrication and use thereof”, filed Dec. 21, 2000 in the names of OskarJ. Painter, Kerry J. Vahala, Peter C. Sercel, and Guido Hunziker, saidprovisional application being hereby incorporated by reference in itsentirety as if fully set forth herein;

[0018] A14) U.S. provisional Application No. 601301,519 entitled“Waveguide-fiber Mach-Zender interferometer and methods of fabricationand use thereof”, filed Jun. 27, 2001 in the names of Oskar J. Painter,David W. Vernooy, and Kerry J. Vahala, said provisional applicationbeing hereby incorporated by reference in its entirety as if fully setforth herein;

[0019] A15) U.S. non-provisional Application No.09/788,303 entitled“Cylindrical processing of optical media”, filed Feb. 16, 2001 in thenames of Peter C. Sercel, Kerry J. Vahala, David W. Vernooy, and GuidoHunziker, said non-provisional application being hereby incorporated byreference in its entirety as if fully set forth herein.

[0020] A16) U.S. non-provisional Application No.09/788,331 entitled“Fiber-ring optical resonators”, filed Feb. 16, 2001 in the names ofPeter C. Sercel, Kerry J. Vahala, David W. Vernooy, Guido Hunziker, andRobert B. Lee, said non-provisional application being herebyincorporated by reference in its entirety as if fully set forth herein.

[0021] A17) U.S. non-provisional Application No. 09/788,300 entitled“Resonant optical filters”, filed Feb. 16, 2001 in the names of Kerry J.Vahala, Peter C. Sercel, David W. Vernooy, Oskar J. Painter, and GuidoHunziker, said non-provisional application being hereby incorporated byreference in its entirety as if fully set forth herein.

[0022] A18) U.S. non-provisional Application No.09/788,301 entitled“Resonant optical power control device assemblies”, filed Feb. 16, 2001in the names of Peter C. Sercel, Kerry J. Vahala, David W. Vernooy,Guido Hunziker, Robert B. Lee, and Oskar J. Painter, saidnon-provisional application being hereby incorporated by reference inits entirety as if fully set forth herein.

[0023] A19) U.S. provisional Application No.______, entitled“Polarization-engineered transverse-optical-coupling apparatus andmethods”, Docket No CQC12P, filed Oct. 30, 2001 in the names of Kerry J.Vahala, Peter C. Sercel, Oskar J. Painter, David W. Vernooy, and DavidS. Alavi, said provisional application being hereby incorporated byreference in its entirety as if fully set forth herein;

[0024] A20) U.S. provisional Application No.60/334,705 entitled“Integrated end-coupled transverse-optical-coupling apparatus andmethods”, Docket No. CQC15P, filed Oct. 30, 2001 in the names of HenryA. Blauvelt, Kerry J. Vahala, Peter C. Sercel, Oskar J. Painter, andGuido Hunziker, said provisional application being hereby incorporatedby reference in its entirety as if fully set forth herein;

[0025] A21) U.S. provisional Application No. 60/333,236 entitled“Alignment apparatus and methods for transverse optical coupling”,Docket No. CQC16P, filed Nov. 23, 2001 in the names of Charles I.Grosjean, Guido Hunziker, Paul M. Bridger, and Oskar J. Painter, saidprovisional application being hereby incorporated by reference in itsentirety as if fully set forth herein;

[0026] A22) U.S. non-provisional Application No.______, entitled“Resonant optical modulators”, Docket No. CQC13NP, filed concurrentlywith the present application in the names of Oskar J. Painter, Peter C.Sercel, Kerry J. Vahala, David W. Vernooy, and Guido Hunziker, saidnon-provisional application being hereby incorporated by reference inits entirety as if fully set forth herein.

[0027] This application is also related to subject matter disclosed inthe following publications, each of said publications being herebyincorporated by reference in its entirety as if fully set forth herein:

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[0040] P13) Carl Arft, Diego R. Yankelovich, Andre Knoesen, Erji Mao,and James S. Harris Jr., “In-line fiber evanescent field electroopticmodulators”, Journal of Nonlinear Optical Physics and Materials Vol.9(1) 79 (2000);

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[0044] P17) H. Saito, T. Makimoto, and N. Kobayashi, “MOVPE growth ofstrained InGaAsN/GaAs quantum wells”, J. Crystal Growth, Vol. 195 416(1998);

[0045] P18) W. G. Bi and C. W. Tu, “Bowing parameter of the band-gapenergy of GaN_(x)As_(1−x)”, Appl. Phys. Lett. Vol. 70(12) 1608 (1997);

[0046] P19) H. P. Xin and C. W. Tu, “GaInNAs/GaAs multiple quantum wellsgrown by gas-source molecular beam epitaxy”, Appl. Phys Lett. Vol.72(19) 2442 (1998);

[0047] P20) B. Koley, F. G. Johnson, O. King, S. S. Saini, and M.Dagenais, “A method of highly efficient hydrolization oxidation of III-Vsemiconductor lattice matched to indium phosphide”, Appl. Phys. Lett.Vol. 75(9) 1264 (1999);

[0048] P21) Z. J. Wang, S.-J. Chua, F. Zhou, W. Wang, and R. H. Wu,“Buried heterostructures InGaAsP/InP strain-compensated multiple quantumwell laser with a native-oxidized InAlAs current blocking layer”, Appl.Phys. Lett. Vol 73(26) 3803 (1998);

[0049] P22) N. Ohnoki, F. Koyama, and K. Iga, “SuperlatticeAlAs/AlInAs-oxide current aperture for long wavelength InP-basedvertical-cavity surface-emitting laser structure”, Appl. Phys. Lett.Vol. 73(22) 3262 (1998);

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[0056] P29) M. H. MacDougal P. D. Dapkus, A. E. Bond, C.-K. Lin, and J.Geske, “Design and fabrication of VCSEL's with Al_(x)O_(y)—GaAs DBR's”,IEEE Journal of Selected Topics in Quantum Electronics Vol. 3(3) 905(1997);

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[0064] Optical fiber and propagation of high-speed optical pulsestherethrough has become the technology of choice for high-speedtelecommunications. Generation of trains of such high-speed opticalpulses, representative of voice, video, data, and/or other signals,requires high-speed optical modulation techniques, typically intensitymodulation techniques. Direct intensity modulation of the light source(usually a laser diode) generally induces unwanted phase and/orfrequency modulation as well, which may be problematic when themodulated optical mode must propagate long distances within the opticalfiber, or when the modulated optical mode is one narrow-linewidthwavelength component among many within a wavelength division multiplexed(WDM) fiber-optic telecommunication system. It has therefore becomestandard practice to provide an external intensity modulator as aseparate optical component, to act on a propagating optical mode afterit has left the light source.

[0065] Other devices may be required for subsequent manipulation and/orcontrol of the propagating optical pulse train, including but notlimited to, for example, routers, switches, fixed and variableattenuators, fixed and variable couplers, bi-directional couplers,channel add-drop filters, N×N switches, and so forth. It is desirablefor these devices to perform their respective functions without the needfor conversion of the optical pulse train into an electronic signal formanipulation and re-conversion to an optical pulse train followingmanipulation. It is preferable for these devices to perform theirrespective functions by direct manipulation of the optical pulse train.To this end many of these devices are fabricated as integrated devices,with optical portions and electronically-driven control portionsfabricated as a single integrated component. Many of these devicesfunction by controlling flow of optical power from one optical mode toanother optical mode in a controlled fashion. For example, optical powermay be shifted from a propagating optical mode of a first optical fiberto a propagating mode of a second optical fiber in anactively-controlled fashion, using so-called directional couplers, or ina wavelength-dependent fashion (active or passive), using so-calledchannel add-drop filters. Application of a control signal to an activedevice may cause optical power to remain within a propagating opticalmode of a first optical fiber, or to couple into a propagating opticalmode of a second optical fiber.

[0066] High insertion losses associated with currently available devicesnecessitate use of optical amplifiers to boost optical signal levels ina fiber-optic telecommunications system, essentially to replace opticalpower thrown away by the use of lossy modulators, couplers, and otherdevices. This adds significantly to the cost, size, and powerconsumption of any fiber-optic system or sub-system. Furthermore, thefull potential of powerful new on-chip integrated optical devices cannotbe realized when a substantial fraction of the optical signal is lostthrough inefficient transfer of optical power between an optical fiberand a waveguide on an integrated optical chip.

[0067] Optical signal power transfer between various optical devices ina fiber-optic telecommunications system relies on optical couplingbetween optical modes in the devices. Transverse-coupling (also referredto as transverse optical coupling, evanescent coupling, evanescentoptical coupling, directional coupling, directional optical coupling)may be employed, thereby eliminating transverse mode matchingrequirements imposed by end-coupling. Such optical power transfer bytransverse-coupling depends in part on the relative modal indices of thetransverse-coupled optical modes. Active control of the modal index ofone or both of the transverse-coupled optical modes would thereforeenable active control of the degree to which optical power istransferred from one device to the other, preferably using controlvoltages substantially smaller magnitude than required by currentlyavailable devices. Optical power transfer from a fiber-optic or otherlow-index optical waveguide to an integrated on-chip optical device(typically higher-index) could be greatly improved by employingtransverse-coupling. Such optical power transfer could be activelycontrolled by controlling a modal index of an optical mode of awaveguide and/or resonator of the integrated device. Optical losseswithin such an integrated on-chip device could also be reduced.

[0068]FIG. 1 shows an example of a modulator 10 fabricated as an opticalwaveguide Mach-Zender interferometer on an electro-optic crystalsubstrate 12 (typically lithium niobate). Standard fabricationtechniques are used to fabricate the waveguide 14 (usually lithographicmasking followed by ion diffusion) and to deposit control electrodes 16.An incident optical signal propagating into entrance face 18 (i.e.,“end-coupled”) and through the device is divided into the two arms ofthe interferometer waveguide 14, application of a control voltage acrossthe control electrodes 16 (in any of several configurations) induces arelative change in the modal indices of the optical modes in the arms(by an electro-optic mechanism), and the optical signals propagating inthe arms are then recombined before exiting through exit face 19.Variation of the control voltage enables modulation of the transmissionof the incident optical signal from a lower operational opticaltransmission level (when the recombined optical modes substantiallydestructively interfere; preferably near zero transmission) to an upperoperational optical transmission level (when the recombined opticalmodes substantially constructively interfere; preferably near 100%transmission, but typically limited by insertion loss of the modulator).Modulators of this sort are widely used in fiber optictelecommunications systems, may enable modulation frequencies up toseveral tens of GHz, and may require control voltages of at leastseveral volts up to about 10 volts for substantially full modulation ofthe optical signal. The control voltage required for a device to achievesubstantially full modulation (i.e., near zero transmission of theoptical mode at the lower transmission level) is referred to as V_(π),since a phase shift of about π is required to make the optical modespropagating in the two arms of the interferometer substantiallydestructively interfere. V_(π) is an important figure-of-merit forcharacterizing electro-optic modulators. The relatively high V_(π) oftypical lithium niobate modulators forces the use of expensive highspeed electronic drivers (described below), increasing cost and powerconsumption of the device. In addition, coupling optical power into andout of the faces of the modulator (end-fire coupling, or end-coupling)is quite inefficient, and typical lithium niobate modulators may haveinsertion losses as high as 6 dB. Most of the insertion loss may beattributed to transverse mode mismatch of the input optical mode and thepreferred mode of the waveguide. This may be somewhat mitigated bymodifying the device to achieve better mode-matching, but at the expenseof a larger V_(π).

[0069]FIG. 2 shows an example of a directional coupler 20 (alsoreferred-to as a 2×2 optical switch) fabricated as an integrated opticaldevice on an electro-optic crystal substrate 22 (typically lithiumniobate). In this example two waveguides 24 a and 24 b are fabricated onthe substrate, and are positioned in relatively close proximity in acoupling portion of the device. In this way an optical signalpropagating in an optical mode of one waveguide may transverse-coupleinto an optical mode of the second waveguide. The device is typicallyconstructed so that over the length of the coupling portion,substantially all of the optical power entering the first waveguide istransferred into the second waveguide. Control electrodes 26 arepositioned so that an applied control voltage alters the relative modalindices of the optical modes of the two waveguides in the couplingportion (by an electro-optic mechanism). A switching voltage V₀,typically several volts up to about 10 volts, is the voltage that altersthe relative modal indices (i.e., the phase matching condition betweenthe waveguides) to the extent that substantially none of the opticalpower entering the first waveguide is transferred to the secondwaveguide. By switching the control voltage between about zero volts andabout V₀, the optical power entering the first waveguide may be switchedbetween exiting via the second waveguide (zero volts applied) or exitingvia the first waveguide (V₀ applied). Such couplers may exhibitswitching frequencies of up to 10 GHz, and V₀ is an importantfigure-of-merit for characterizing electro-optic couplers. In a mannersimilar to the modulators described hereinabove, these devices requirecostly high-speed electronic driver hardware (described below) andexhibit insertion losses as high as 6 dB.

[0070] A general discussion of electro-optic modulators,interferometers, and couplers may be found in Fundamentals of Photonicsby B. E. A. Saleh and M. C. Teich (Wiley, New York, 1991), herebyincorporated by reference in its entirety as if fully set forth herein.Particular attention is called to Chapter 18.

[0071] For operating voltages (V_(π) or V₀) on the order of severalvolts and high modulation/switching frequencies, a high speed electroniccontrol input signal must typically be amplified to the appropriatelevel for application to the device by a high speed electronicamplifier, usually referred to as a driver or RF driver. A driver addssubstantially to the size, cost, and power consumption of currentoptical modulators, couplers, and other devices, and may limit themaximum frequency at which such devices may be driven. For operatingvoltages (V_(π) or V₀) on the order of 10 V, a device may consume on theorder of 1 W of electrical drive power. This power must be dissipatedand/or otherwise managed properly to avoid overheating, degradedperformance, and/or eventual failure of the device. This may beparticularly problematic when the properties defining the performance ofthe device (such as waveguide pathlength, refractive and modal indices,and so forth) are temperature dependent. Since such large numbers ofsuch modulators, couplers, switches, and other optical devices arerequired to implement a fiber-optic telecommunications system of anysignificant extent (organization-, city-, state-, nation-, and/orworld-wide; alternatively enterprise, metro, and/or trunk systems), anypotential reductions in size, cost, and/or power consumption may proveto be quite significant. A sub-volt control voltage level (V_(π) and/orV₀) would eliminate the need for a driver, potentially cutting the costof each device, and would result in a corresponding decrease in powerconsumption and its attendant technical difficulties and economicdisadvantages. Limitations on operating speed imposed by driverperformance would be eliminated.

[0072] It is desirable to provide optical modulators, interferometers,couplers, routers, add/drop filters, switches, and/or other deviceswherein optical power may be efficiently transferred to/from the devicefrom/to an optical fiber or other low-index waveguide withoutlimitations and/or insertion losses imposed by end-coupling. It isdesirable to provide optical modulators, interferometers, couplers,routers, add/drop filters, switches, and/or other devices whereinoptical power may be efficiently transferred to/from the device from/toan optical fiber or other low-index waveguide by transverse-coupling. Itis desirable to provide optical modulators, interferometers, couplers,routers, add/drop filters, switches, and/or other devices havinginsertion loss less than about 3 dB. It is desirable to provide opticalmodulators, interferometers, couplers, routers, add-drop filters,switches, and/or other integrated optical devices that may be wellmodal-index-matched to optical fiber and/or other low-index waveguides.It is desirable to provide optical modulators, interferometers,couplers, routers, add-drop filters, and/or other devices that may befabricated as integrated optical devices, on a planar platform or onmultiple-level vertically-integrated planar platforms. It is thereforedesirable to provide optical modulators, interferometers, couplers,routers, add-drop filters, switches, and/or other devices wherein therequired control voltage level (V_(π) or V₀) is less than about onevolt. It is desirable to provide optical modulators, interferometers,couplers, routers, add-drop filters, and/or other devices that do notrequire a driver for amplifying electronic control signals. It isdesirable to provide optical modulators, interferometers, couplers,routers, add-drop filters, and/or other devices that are compatible withother extant components of a fiber-optic telecommunications system.

SUMMARY

[0073] Certain aspects of the present invention may overcome one or moreaforementioned drawbacks of the previous art and/or advance thestate-of-the-art of apparatus and methods for modulating, routing,and/or other optical power control devices, and in addition may meet oneor more of the following objects:

[0074] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof compatible with otherextant components of a fiber-optic telecommunications system;

[0075] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof that may befabricated as integrated optical devices;

[0076] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof that may yieldoptical devices having insertion loss of less than about 3 dB;

[0077] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein optical powermay be efficiently transferred to/from the device from/to an opticalfiber or other low-index waveguide;

[0078] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof whereintransverse-coupling serves to transfer optical signals to/from thewaveguide/resonator;

[0079] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof that may include alaterally-confined optical waveguide segment;

[0080] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof that may include amulti-layer optical waveguide segment;

[0081] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof that may include adispersion-engineered waveguide segment;

[0082] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof that may include aridge-like waveguide/resonator structure protruding from a substrate;

[0083] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof for enablingmodal-index-matching between the waveguide/resonator and an opticalfiber or other low-index waveguide;

[0084] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof for enabling passivemodal-index-matching between the waveguide/resonator and an opticalfiber or other low-index waveguide;

[0085] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof for enabling activemodal-index-matching between the waveguide/resonator and an opticalfiber or other low-index waveguide by application of a control signal tothe waveguide/resonator;

[0086] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein a multi-layerstack guides a surface-guided optical mode, the surface-guided opticalmode being transverse-coupled to a mode of another optical element;

[0087] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein a pair ofmulti-layer stacks guide a substantially confined optical modetherebetween, the confined optical mode being transverse-coupled to amode of another optical element;

[0088] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein thewaveguide/resonator includes an at least one electro-active layer andelectronic control components for controlling the electro-active layer;

[0089] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein thedispersive properties of the multi-layer stack(s) enable substantialchanges in the modal index and/or modal loss of a guided optical mode byapplication of relatively small control voltages to the electro-activelayer;

[0090] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein thewaveguide/resonator includes at least one non-linear-optical layer andoptical control components for controlling the non-linear-optical layer;

[0091] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein thedispersive properties of the multi-layer stack(s) enable substantialchanges in the modal index and/or modal loss of a guided optical mode byapplication of relatively small optical control signals to thenon-linear-optical layer;

[0092] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein the requiredcontrol voltage level (V_(π) or V₀) may be less than about one volt;

[0093] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein use of adriver for amplifying high-data-rate electronic control signals may notbe required;

[0094] To provide fiber-optic modulators and methods of fabrication anduse thereof wherein a simplified driver for amplifying high-data-rateelectronic control signals may be employed;

[0095] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein thewaveguide/resonator further comprises lateral lower-index portions forsubstantially laterally confining a guided optical mode;

[0096] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein laterallower-index portions of the waveguide/resonator restrict the guidedoptical modes to one or a few transverse optical modes;

[0097] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein laterallower-index portions of the waveguide/resonator decrease optical lossand/or increase the Q-factor of the waveguide/resonator;

[0098] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein themulti-layer stack(s), electro-active and/or non-linear-optical layer,and control components (if present) may be fabricated by a layergrowth/deposition sequence on a single substrate;

[0099] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein themulti-layer stack(s), electro-active and/or non-linear-optical layer,and control components (if present) may be fabricated by layergrowth/deposition sequences on multiple substrates followed bywafer-bonding of the grown/deposited layers;

[0100] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein laterallow-index portions of the waveguidel resonator may be provided bylateral chemical conversion of one or more layers of thewaveguide/resonator;

[0101] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein one or moregrown/deposited layers of the waveguide/resonator may subsequently besubstantially completely converted to another material through lateralchemical conversion;

[0102] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein control of amodal index of a guided optical mode enables control of optical powertransfer between the waveguide/resonator and another optical elementthrough transverse-coupling;

[0103] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein control of amodal index of a guided resonant optical mode enables control of aresonance frequency of the resonator; and

[0104] To provide waveguides and resonators for integrated opticaldevices and methods of fabrication and use thereof wherein control of amodal index and/or optical loss of a guided optical mode enables controlof an operational state of the optical device.

[0105] One or more of the foregoing objects may be achieved in thepresent invention by an optical waveguide/resonator including at leastone multi-layer laterally-confined dispersion-engineered opticalwaveguide segment. The multi-layer waveguide segment may include asingle multi-layer reflector stack for guiding a surface-guided opticalmode (SGOM). The multi-layer waveguide segment may also include laterallower-index portions thereof for lateral confinement of thesurface-guided optical mode, and may include a waveguide or core layerthereon. The multi-layer waveguide segment may further comprise one ormore electro-active and/or non-linear-optical layers and controlcomponents for controlling the refractive index and/or optical lossthereof. Strongly dispersive optical properties of thesingle-reflector-guided SGOM (a substantially flat dispersion relationin the operating wavelength range, so that a narrow range of wavelengthscover a wide range of propagation constants or modal indices) serve toproduce a substantially larger modal index shift of the SGOM for a givenapplied control signal than previous devices. The surface-guided opticalmode may be transverse-coupled to another optical mode of anotheroptical element. Control of the modal index and/or optical loss mayenable control of: optical power transfer between thewaveguide/resonator and another optical element; the resonance frequencyof a resonant optical mode of a resonator; and an operational state ofthe waveguide/resonator and/or an optical device incorporating thewaveguide/resonator.

[0106] Alternatively, the multi-layer waveguide segment may include apair of multi-layer reflector stacks for guiding a substantiallyconfined optical mode along a waveguide or core layer therebetween. Sucha dual-reflector waveguide segment may also include lateral lower-indexportions thereof for lateral confinement of the guided optical mode. Thedual-reflector waveguide segment may further comprise one or moreelectro-active and/or non-linear-optical layers and control componentsfor controlling the refractive index and/or optical loss thereof. Thestrongly dispersive optical properties of the dual-reflector-guidedoptical mode (a substantially flat dispersion relation in the operatingwavelength range, so that a narrow range of wavelengths cover a widerange of propagation constants or modal indices) serve to produce asubstantially larger modal index shift of the guided optical mode for agiven applied control signal than previous devices. The guided opticalmode may be transverse-coupled to another optical mode of anotheroptical element. Control of the modal index and/or optical loss mayenable control of: optical power transfer between thewaveguide/resonator and another optical element; the resonance frequencyof a optical mode of a resonator; and an operational state of thewaveguide/resonator and/or an optical device incorporating thewaveguide/resonator.

[0107] Multi-layer waveguides/resonators may be fabricated by 1)“vertical fabrication” of a multi-layer structure including reflectorstack(s), any required core or waveguide layer, any requiredelectro-active and/or non-linear-optical layer(s), any required controlcomponents, and any other desired layers on a substrate, followed by 2)“horizontal fabrication” of the multi-layer structure byspatially-selective processing of portions of the multi-layer structure,creating on the substrate a multi-layer waveguide segment of the desiredsize, shape, and topology. The “horizontal fabrication” step may furtherinclude lateral processing of one or more layers of the multi-layerwaveguide segment, resulting in chemical conversion of all or part ofthe affected layers.

[0108] Additional objects and advantages of the present invention maybecome apparent upon referring to the preferred and alternativeembodiments of the present invention as illustrated in the drawings anddescribed in the following written description and/or claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0109] In many of the Figures, a reference coordinate system is shownfor descriptive convenience only.

[0110]FIG. 1 shows a prior-art Mach-Zender interferometer modulatorfabricated on an electro-optic crystal substrate.

[0111]FIG. 2 shows a prior-art directional coupler fabricated on anelectro-optic crystal substrate.

[0112]FIGS. 3A, 3B, and 3C are top plan, transverse-sectional, and sideelevation views, respectively, of an optical waveguide on a substrateaccording to the present invention, showing a direction of lightpropagation therein.

[0113]FIG. 4 is an isometric view of an optical waveguide on a substrateaccording to the present invention, showing a direction of lightpropagation therein.

[0114]FIGS. 5A, 5B, and 5C are top plan, transverse-sectional, and sideelevation views, respectively, of an optical resonator on a substrateaccording to the present invention, showing a direction of lightpropagation therein.

[0115]FIG. 6 is an isometric view of an optical resonator on a substrateaccording to the present invention, showing a direction of lightpropagation therein.

[0116]FIG. 7 is a transverse-sectional view of a single-DBR waveguide ofthe present invention positioned on a substrate.

[0117]FIG. 8 is a transverse-sectional view of a single-DBR waveguide ofthe present invention, having a core layer thereon and positioned on asubstrate.

[0118]FIG. 9 is a transverse-sectional view of an asymmetric-dual-DBRwaveguide of the present invention positioned on a substrate.

[0119]FIG. 10 is a transverse-sectional view of a dual-DBR waveguide ofthe present invention positioned on a substrate.

[0120]FIG. 11 is a transverse-sectional view of a single-DBR waveguideof the present invention, having lateral low-index portions thereon andpositioned on a substrate.

[0121]FIG. 12 is a transverse-sectional view of a single-DBR waveguideof the present invention, having a core layer and lateral low-indexportions thereon and positioned on a substrate.

[0122]FIG. 13 is a transverse-sectional view of an asymmetric-dual-DBRwaveguide of the present invention, having lateral low-index portionsthereon and positioned on a substrate.

[0123]FIG. 14 is a transverse-sectional view of a dual-DBR waveguide ofthe present invention, having lateral low-index portions thereon andpositioned on a substrate.

[0124]FIG. 15 is a flow diagram for a single-substrate verticalfabrication procedure for a single-DBR waveguide of the presentinvention.

[0125]FIG. 16 is a process diagram for a single-substrate verticalfabrication procedure for a single-DBR waveguide of the presentinvention.

[0126]FIG. 17 is a flow diagram for a single-substrate verticalfabrication procedure for a single-DBR waveguide of the presentinvention.

[0127]FIG. 18 is a process diagram for a single-substrate verticalfabrication procedure for a single-DBR waveguide of the presentinvention.

[0128]FIG. 19 is a flow diagram for a single-substrate verticalfabrication procedure for a single-DBR waveguide of the presentinvention.

[0129]FIG. 20 is a process diagram for a single-substrate verticalfabrication procedure for a single-DBR waveguide of the presentinvention.

[0130]FIG. 21 is a flow diagram for a two-substrate vertical fabricationprocedure for a single-DBR waveguide of the present invention.

[0131]FIG. 22 is a process diagram for a two-substrate verticalfabrication procedure for a single-DBR waveguide of the presentinvention.

[0132]FIG. 23 is a flow diagram for a two-substrate vertical fabricationprocedure for a single-DBR waveguide of the present invention.

[0133]FIG. 24 is a process diagram for a two-substrate verticalfabrication procedure for a single-DBR waveguide of the presentinvention.

[0134]FIG. 25 is a flow diagram for a two-substrate vertical fabricationprocedure for a single-DBR waveguide of the present invention.

[0135]FIG. 26 is a process diagram for a two-substrate verticalfabrication procedure for a single-DBR waveguide of the presentinvention.

[0136]FIG. 27 is a flow diagram for a single-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0137]FIG. 28 is a process diagram for a single-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0138]FIG. 29 is a flow diagram for a single-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0139]FIG. 30 is a process diagram for a single-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0140]FIG. 31 is a flow diagram for a single-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0141]FIG. 32 is a flow diagram for a single-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0142]FIG. 33 is a flow diagram for a single-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0143]FIG. 34 is a process diagram for a single-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0144]FIG. 35 is a flow diagram for a three-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0145]FIG. 36 is a process diagram for a three-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0146]FIG. 37 is a flow diagram for a three-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0147]FIG. 38 is a process diagram for a three-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0148]FIG. 39 is a flow diagram for a three-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0149]FIG. 40 is a process diagram for a three-substrate verticalfabrication procedure for a dual-DBR waveguide of the present invention.

[0150]FIGS. 41A and 41B are process diagrams for horizontal fabricationof a waveguide of the present invention.

[0151]FIGS. 42A and 42B are process diagrams for horizontal fabricationof a resonator of the present invention.

[0152]FIGS. 43A and 43B are process diagrams for horizontal fabricationof a resonator of the present invention.

[0153]FIG. 44 is a process diagram for horizontal fabrication of awaveguide of the present invention.

[0154]FIG. 45 is a process diagram for horizontal fabrication of awaveguide of the present invention.

[0155]FIG. 46 is a process diagram for horizontal fabrication of awaveguide of the present invention.

[0156]FIG. 47 is a process diagram for horizontal fabrication of awaveguide of the present invention.

[0157]FIG. 48 is a process diagram for horizontal fabrication of awaveguide of the present invention.

[0158]FIG. 49 is a transverse-sectional view of a waveguide of thepresent invention having asymmetric lateral low-index portions thereon.

[0159]FIG. 50 is a transverse-sectional view of a waveguide of thepresent invention having asymmetric lateral low-index portions thereon.

[0160]FIG. 51 shows a fiber-optic taper transverse-coupled to an opticalwaveguide on a substrate according to the present invention.

[0161]FIG. 52 shows a Mach-Zender interferometer optical modulator on asubstrate according to the present invention.

[0162]FIG. 53 shows a fiber-optic taper transverse-coupled to aMach-Zender interferometer optical modulator on a substrate according tothe present invention.

[0163]FIG. 54 shows a fiber-optic taper transverse-coupled to aMach-Zender interferometer optical modulator on a substrate according tothe present invention.

[0164]FIG. 55 shows an optical switch on a substrate according to thepresent invention.

[0165]FIG. 56 shows a pair of fiber-optic tapers transverse-coupled toan optical switch on a substrate according to the present invention.

[0166]FIG. 57 shows a fiber-optic taper transverse-coupled to an opticalresonator on a substrate in turn transverse-coupled to a loss-controloptical waveguide according to the present invention.

[0167]FIGS. 58 and 59 show a fiber-optic taper transverse-coupled to anoptical waveguide on a substrate according to the present invention soas to form a Mach-Zender interferometer optical modulator.

[0168]FIGS. 60 and 61 show a fiber-optic taper transverse-coupled to anoptical waveguide on a substrate according to the present invention soas to form a Mach-Zender interferometer optical modulator.

[0169]FIG. 62A and 62B show examples of multi-layer and/or periodicstructures employed for lateral confinement of a guided optical mode ina waveguide.

[0170] It should be noted that the relative proportions of variousstructures shown in the Figures may be distorted to more clearlyillustrate the present invention. In particular, various metal,semiconductor, and/or other thin films, layers, and/or coatings may alsobe shown having disproportionate and/or exaggerated thicknesses forclarity. Relative dimensions of various waveguides, resonators, opticalfibers/tapers, and so forth may also be distorted, both relative to eachother as well as transverse/longitudinal proportions. The text andincorporated references should be relied on for the appropriatedimensions of structures shown herein.

DETAILED DESCRIPTION OF PREFERRED AND ALTERNATIVE EMBODIMENTS

[0171] For purposes of the present written description, the term“waveguide” shall often be intended encompass both open waveguides (inwhich no closed optical path is provided for allowing re-circulation ofoptical power within an optical mode supported by the waveguide) andclosed waveguides (in which a closed optical path is provided forallowing re-circulation of optical power within an optical modesupported by the waveguide; such closed waveguides may also beequivalently referred to as resonators or rings). The term “waveguide”shall often be used herein to denote both open and closed structureswhen structure and/or fabrication of such open and closed waveguides isdiscussed. In portions of the written description wherein only one orthe other type of waveguide (open or closed) is described, it will bemade clear in the text which is intended, either implicitly orexplicitly. This will typically be the case when functional aspects ofdevices incorporating the open and/or closed waveguides are discussed.

[0172] For purposes of the present written description and/or claims,the term “laterally-confined waveguide” shall typically denote anoptical structure elongated along an optical propagation direction (thelongitudinal direction) and adapted so as to substantially confine oneor more optical modes in directions substantially perpendicular to theoptical propagation direction (i.e., transverse directions). Thelongitudinal dimension/direction shall be associated with the terms“forward”, “backward”, and so on. Such laterally-confined waveguides arefrequently fabricated on, mounted on, or otherwise positioned on asubstantially planar portion of a substrate, in which case longitudinaldimensions/directions may also be referred to as “horizontal”.Transverse dimensions/directions may be associated with terms “vertical”and “horizontal” relative to a substrate. Vertical dimensions/directions(hence also transverse relative to the waveguide) may be associated withthe terms “up”, “down”, “above”, “below”, “superior”, “inferior”, “top”,“bottom”, and so on. Horizontal dimensions/directions that are alsotransverse relative to the waveguide may be associated with the terms“left”, “right”, “lateral”, “medial”, “side”, and so on. Suchdescriptive terms are typically intended to convey local directionsand/or positions relative to a waveguide, a substrate, an alignmentstructure, and/or the like, and are typically not intended to conveyabsolute position or direction in space.

[0173] An example configuration of an open waveguide 30 on a substrate32 is shown in FIGS. 3A, 3B, 3C, and 4, while an example configurationof a resonator 50 on substrate 52 is shown in FIGS. 5A, 5B, 5C, and 6.As shown in these Figures, a reference axis system may be definedrelative to a waveguide or resonator structure on a substrate forconvenience of description only, and shall not be construed as limitingthe scope of inventive concepts disclosed and/or claimed herein. The+z-axis shall be defined generally as the direction of propagation oflight along a waveguide or resonator structure (indicated by the largeropen arrows), and will typically be oriented substantially parallel to aplane defined by the substrate surface on which the waveguide orresonator is positioned. It should be noted that such waveguide orresonator structures may typically support propagation of light ineither direction (i.e., +z or −z). The +y-axis shall be orientedsubstantially perpendicular to and away from the substrate surfaceplane. The x-axis shall be oriented substantially parallel to thesubstrate plane and substantially perpendicular to the direction ofpropagation of light along the waveguide or resonator. The referenceaxis system is defined locally with respect to the waveguide orresonator, so that in the case of a curved waveguide or resonator, theaxis system may vary in its absolute orientation in space at variouspoints along the waveguide or resonator, but its orientation withrespect to the waveguide at any given point is substantially asdescribed hereinabove (note FIGS. SA, 5B, 5C, and 6). The z-directionmay be referred to as the longitudinal direction. The x-direction may bereferred to as transverse, horizontal, left, right, lateral, and/ormedial, while the y-direction may be referred to as transverse,vertical, up, down, superior, and/or inferior.

[0174] For purposes of the written description and/or claims, “index”may denote the bulk refractive index of a particular material (alsoreferred to herein as a “material index”) or may denote the propagationconstant (in the z-direction) of a particular optical mode in aparticular optical element (referred to herein as a “modal index”). Asreferred to herein, the term “low-index” shall denote any materialsand/or optical structures having an index less than about 2.5, while“high-index” shall denote any materials and/or structures having anindex greater than about 2.5. Within these bounds, “low-index” maypreferably refer to silicas, glasses, oxides, polymers, and any otheroptical materials having indices between about 1.3 and about 1.8, andmay include optical fiber, optical waveguides, planar lightwave circuitcomponents, and any other optical components incorporating suchmaterials. Similarly, “high-index” may preferably refer to materialssuch as semiconductors or any other material having indices of about 3or greater. The terms “high-index” and “low-index” are to bedistinguished from the terms “lower-index” and “higher-index”, alsoemployed herein. “Low-index” and “high-index” refer to an absolutenumerical value of the index (greater than or less than about 2.5),while “lower-index” and “higher-index” are relative terms indicatingwhich of two materials has the larger index, regardless of the absolutenumerical values of the indices.

[0175] For purposes of the written description and/or claims, the term“multi-layer reflector stack” or “MLR stack” or “MLR” shall denote amulti-layer structure wherein the layer index varies with eachsuccessive layer of the stack (typically alternately increasing anddecreasing; often alternating layers of a higher-index material and alower-index material), yielding an optical structure havingwavelength-dependent optical properties. A common example of such astructure is a distributed Bragg reflector (DBR), which may typicallycomprise alternating quarter-wave-thickness layers of a higher-indexmaterial and a lower-index material. Graded-index material(s) may alsobe employed. The term “multi-layer reflector stack” shall denote anyperiodic, partially periodic, multi-periodic, quasi-periodic, and/orsimilar multi-layer varying-index structure.

[0176] For purposes of the written description and/or claims, the term“electro-active” shall denote any material that may exhibitelectro-optic and/or electro-absorptive properties. The term“non-linear-optical” shall denote any material that may exhibitnon-linear optical properties, including both resonant and non-resonantnon-linear-optical properties.

[0177] For purposes of the written description and/or claims,“transverse-coupling” (also referred to as transverse optical coupling,evanescent coupling, evanescent optical coupling, directional coupling,directional optical coupling) shall generally denote those situations inwhich two optical elements, each capable of supporting a propagatingand/or resonant optical mode and at least one having an evanescentportion of its optical mode extending beyond the respective opticalelement, are optically coupled by at least partial transverse spatialoverlap of the evanescent portion of one optical mode with at least aportion of the other optical mode. The amount, strength, level, ordegree of optical power transfer from one optical element to the otherthrough such transverse optical coupling depends on the spatial extentof the overlap (both transverse and longitudinal), the spectralproperties of the respective optical modes, and the relative spatialphase matching of the respective optical modes (also referred to asmodal index matching). To transfer optical power most efficiently, therespective modal indices of the optical modes (equivalently, therespective modal propagation constants), each in its respective opticalelement, must be substantially equal. Mismatch between these modalindices decreases the amount of optical power transferred by transversecoupling between the optical elements, since the coupled modes getfurther out of phase with each other as each propagates within itsrespective optical element and the direction of the optical powertransfer eventually reverses itself. The propagation distance over whichthe modes interact (i.e., the effective interaction length) and thedegree of modal-index matching (or mismatching) together influence theoverall flow of optical power between the coupled modes. Optical powertransfer between the coupled modes oscillates with a characteristicamplitude and spatial period as the modes propagate, each in itsrespective optical element.

[0178] Neglecting the effects of optical loss in the optical elements,an ideal system consisting of two coupled modes can be characterized bythe following coupled system of equations:$\frac{\partial E_{1}}{\partial z} = {{i\quad \beta_{1}E_{1}} + {i\quad \kappa \quad E_{2}}}$$\frac{\partial E_{2}}{\partial z} = {{i\quad \beta_{2}E_{2}} + {i\quad \kappa^{*}E_{1}}}$

[0179] where the following definitions apply:

[0180] E_(1, 2) amplitudes of the coupled fields;

[0181] β_(1, 2) propagation constants of the coupled fields;

[0182] κ coupling amplitude resulting from spatial overlap of thefields;

[0183] z propagation distance coordinate.

[0184] For the purpose of illustration, it is assumed that the couplingamplitude κ is constant over an interaction distance L. Then, anincident field of amplitude E₁ that is spatially confined to the firstoptical element before interaction will couple to the other wave guidewith a resultant field amplitude E₂(L) at z=L (where we define z=0 asthe start of the coupling region) given by the following expression,$\frac{{{E_{2}(L)}}^{2}}{{{E_{l}(0)}}^{2}} = {\frac{{\kappa }^{2}}{q^{2}}\sin^{2}\quad \left( {q\quad L} \right)}$$q^{2} = {{\kappa }^{2} + {\frac{1}{4}\Delta \quad {\beta^{2}.}}}$

[0185] Consider the modal-index mismatch term (Δβ=β₂−β₁) and theinteraction length in this expression. As is well known, a condition ofmodal-index mismatch between the two spatial modes causes an oscillatorypower transfer to occur between the waveguides as the interaction lengthis varied. The spatial period of this oscillation, a so-called “beatlength”, can be defined as the distance over which power cycles back andforth between the guides. Greater amounts of modal-index mismatch willreduce the beat length. Also note that the absolute magnitude of powertransfer will diminish with increasing modal-index mismatch. Finally, itis apparent that increased amounts of interaction length and/orincreased modal-index mismatch will introduce an increased spectralselectivity to the optical power transfer.

[0186] By controlling the modal-index mismatch and/or transverse spatialoverlap between optical modes, these characteristics may be exploitedfor controlling optical power transfer between optical elements. Forexample, by altering the modal-index mismatch, a device may be switchedfrom a first condition, in which a certain fraction of optical power istransferred from a first optical mode in a first optical element to asecond optical mode in a second optical element (modal-index mismatchset so that the effective interaction length is about half of thecharacteristic spatial period described above), to a second condition inwhich little or no optical power is transferred (modal-index mismatchset so that the effective interaction length is about equal to thecharacteristic spatial period). Further discussion of optical couplingmay be found in Fundamentals of Photonics by B. E. A. Saleh and M. C.Teich (Wiley, New York, 1991), hereby incorporated by reference in itsentirety as if fully set forth herein. Particular attention is called toChapters 7 and 18.

[0187] It should be noted that optical waveguides and resonators asdescribed herein, optical modulators, interferometers, couplers,routers, add-drop filters, switches, and other devices incorporatingsuch waveguides and/or resonators, their fabrication, and their useaccording to the present invention are intended primarily for handlingoptical modes having wavelengths between about 0.8 μm and about 1.0 μm(the wavelength range typically utilized for so-called short-haulfiber-optic telecommunications) and optical modes having wavelengthsbetween about 1.2 μm and about 1.7 μm (the wavelength range typicallyutilized for so-called long-haul fiber-optic telecommunications).However, these devices, methods of fabrication, and methods of use maybe adapted for use at any desired wavelength while remaining within thescope of inventive concepts disclosed and/or claimed herein.

[0188] Optical waveguides and/or resonators according to the presentinvention may typically fall into one of two general categories, or mayfall into an intermediate category. In the first category, illustratedschematically in transverse-section in FIG. 7, the waveguide structure700 comprises a single multi-layer reflector 702 (equivalently, a MLR orMLR stack), shown in the form of an elongated ridge-like structureprotruding from a substrate 710. This category may also include awaveguide structure 800 as shown schematically in transverse section inFIG. 8, comprising a MLR stack 802 and a core or waveguide layer 804 onsubstrate 810. Such a single-MLR waveguide may support propagation of anoptical mode as a surface-guided optical mode (equivalently, a SGOM, SGOmode, SG mode, surface-guided mode, optical SGM, SGM, or SG opticalmode; such modes have been referred to in the literature assurface-guided Bloch modes (SGBM), anti-resonant reflecting opticalwaveguide modes (ARROW), and so forth). Such an optical mode is confinedand guided from below by the reflectivity of the MLR stack 702 (802),and from above by the index contrast between the MLR stack 702 (corelayer 804) and a surrounding lower-index medium (air; vacuum; alower-index glass, polymer, semi-conductor, electro-optic, or otherover-layer). Lateral confinement of the SGOM may arise from a similarindex contrast between the sides of an elongated, ridge-like MLR stack702 (MLR stack 802 and core layer 804) and a surrounding lower-indexmedium. Alternatively, some or all of the MLR layers may be providedwith uni-lateral and/or bilateral lower-index portions for laterallyconfining the SGOM within the MLR stack, as shown schematically intransverse-section in FIGS. 11 and 12. FIG. 11 shows a waveguide 1100 onsubstrate 1110, waveguide 1100 comprising a single MLR stack 1102 andlateral lower-index portions 1103. FIG. 12 shows a waveguide 1200 onsubstrate 1210, waveguide 1200 comprising a single MLR stack 1202,lateral lower-index portions thereof 1203, core layer 1204, and laterallower-index portions thereof 1205. In FIG. 12, one or the other or bothof MLR stack 1202 and core layer 1204 may be provided with respectivelower-index lateral portions 1203 and 1205. Lateral confinement mayalternatively be provided by lateral metallic coatings, lateraldielectric coatings, lateral multi-layer reflectors or distributed Braggreflectors, and/or internal reflection at a waveguide lateral surface.In any of FIGS. 7, 8, 11, or 12, evanescent portions of the SG opticalmode may extend upward from the top of the MLR stack and/or laterallyfrom one or both sides of the MLR stack, thereby enablingtransverse-coupling between the SG optical mode and other optical modessufficiently near the top and/or sides of the single-MLR stack.

[0189] In the second category of waveguides and/or resonators,illustrated schematically in transverse-section in FIG. 10, waveguide1000 comprises a pair of MLR stacks 1002 and 1006 are employed toconfine and guide a propagating optical mode, one from above and onefrom below (referred to hereinafter as a dual-MLR stack). The two MLRstacks (which may or may not be substantially similar), as well as awaveguide layer 1004 (alternatively, a “core” layer) providedtherebetween (along which the propagating optical mode is substantiallyconfined), are shown in the form of an elongated ridge-like structureprotruding from a substrate 1010. Lateral confinement of the opticalmode may arise in a manner similar to that described in the precedingparagraph, either by index contrast between the waveguide structure 1000and a surrounding lower-index medium, or by lateral (uni-lateral and/orbilateral) lower-index portions provided in some or all of the layers ofthe MLR stacks and/or waveguide layer, which substantially confine theoptical mode within the dual-MLR waveguide structure, as shownschematically in transverse-section in FIG. 14. FIG. 14 shows awaveguide 1400 on substrate 1410, waveguide 1400 comprising bottom MLRstack 1402 with lower-index portions 1403, core layer 1404 withlower-index portions 1405, and top MLR stack 1406 with lower-indexportions 1407. In FIG. 14, one, any two, or all three of MLR stacks 1402and 1406 and core layer 1404 may be provided with respective lower-indexlateral portions 1403, 1407, and 1405. Lateral confinement mayalternatively be provided by lateral metallic coatings, lateraldielectric coatings, lateral multi-layer reflectors or distributed Braggreflectors, and/or internal reflection at a waveguide lateral surface.In either FIG. 10 or FIG. 14, evanescent portions of the optical modemay extend laterally from one or both sides of the waveguide layer,thereby enabling transverse-coupling between the optical mode and otheroptical modes propagating sufficiently near a side of the dual-MLR stackwaveguide structure.

[0190] Intermediate between these two categories are structurescomprising a lower MLR stack, a waveguide or core layer, and a partialupper MLR stack. Such structures shall be referred to herein as partialdual-MLR stack waveguide structures, and are shown schematically intransverse-section in FIGS. 9 and 13. In FIG. 9, waveguide 900 (onsubstrate 910) comprises a lower MLR 902, and core layer 904, and apartial upper MLR 906. In FIG. 13, waveguide 1300 (on substrate 1310)comprises a lower MLR 1302 with lateral lower-index portions thereof1303, core layer 1304 with lateral lower-index portions thereof 1305,and partial upper MLR 1306 with lateral lower-index portions thereof1307. In FIG. 13, any one, any two, or all three of MLR stacks 1302 and1306 and core layer 1304 may be provided with respective lower-indexlateral portions 1303, 1307, and 1305. Such structures provide a rangeof behaviors intermediate between the single-MLR structures (wherein thesupported optical mode has a substantially fully accessible evanescentportion extending upward from the top of the waveguide) and the dual-MLRstructures (wherein substantially no evanescent portion of the supportedoptical mode extends upward from the top of the waveguide). Providing apartial upper MLR stack allows the extent of the evanescent portion ofthe supported optical mode extending upward from the top of thewaveguide to be tailored to fit a particular application by varying thenumber and characteristics of the layers comprising the partial upperMLR stack.

[0191] The exemplary transverse waveguide structures illustrated inFIGS. 7-14 are shown having layers of the multi-layer reflector stackssubstantially parallel to the substrate and providing confinement of aguided optical mode along a vertical direction. It is also possible andmay be desirable to construct, fabricate, assemble, or otherwise providewaveguides having layers of one or more multi-layer reflector stackssubstantially perpendicular to the substrate, thereby providingconfinement of a guided optical mode along a horizontal direction. Anexample of such a structure is shown in transverse section in FIG. 62A,including MLR stacks 6202 surrounding a core 6206, all positioned onsubstrate 6210. It may be desirable to construct, fabricate, assemble,or otherwise provide waveguides having multi-layer stacks with layers inboth substantially parallel and substantially perpendicularorientations, so as to provide confinement of a guided optical modealong both horizontal and vertical directions. Alternatively, it may bedesirable to provide one or more layers of a multi-layer waveguidestructure with a grating. Such a grating may serve to provide lateralconfinement for a support optical mode, and may also cause the waveguideto exhibit desirable dispersive properties. An example of such awaveguide is shown in transverse section in FIG. 62B positioned on asubstrate 6219. Core layer 6220 is provided with a central portion 6222(along which a guided mode may propagate) and lateral grating portions6224. Upper and lower clad layers 6230 are provided below and, ifdesired, above core layer 6220, and may comprise a single layer oflower-index material or a MLR stack. Upper and lower layers 6230 serveto confine a guided optical mode vertically, while grating portions 6224of core layer 6220 serve to confine the guided optical modehorizontally. Grating portions 6224 may be provided using any suitablespatially-selective material processing techniques.

[0192] Part of the utility of MLR-based waveguide structures inwaveguides and/or resonators incorporated into optical devices arisesfrom their dispersive optical properties, which enabledispersion-engineering of the devices. A MLR waveguide exhibits asubstantially flat dispersion relation for guided optical modes overmid-IR, near-IR, and visible wavelengths, so that a narrow range ofwavelengths spans a wide range of propagation constants (equivalently, awide range of modal indices). This may be exploited in a variety ofways. A waveguide incorporating a MLR structure may be used tomodal-index-match to another optical component having a substantiallydifferent refractive index. Such modal-index-matching may be achieved byappropriate and accurate design and fabrication of the multi-layerreflector (so-called passive modal-index-matching). Alternatively, anelectrical or optical signal may be applied to a multi-layer reflectorincorporating one or more electro-active or non-linear-optical layers,respectively, to achieve modal-index-matching over a substantial rangeof modal-indices (so-called active modal-index-matching).

[0193] Waveguide and/or resonator structures as described in thepreceding paragraphs may find widely applicable utility in the fields offiber-optic telecommunications and sensors and integrated opticaldevices. Optical power transfer between various optical devices in afiber-optic telecommunications system frequently rely on opticalcoupling between optical modes in the devices. Transverse-coupling maybe employed, thereby eliminating spatial-mode-matching requirementsimposed by end-coupling. Optical signal power transfer bytransverse-coupling depends in part on the relative modal indices of thetransverse-coupled optical modes. Active control of the modal index ofone or both of the transverse-coupled optical modes therefore enablesactive control of the degree to which optical signal power istransferred from one device to the other. If one of the devices to becoupled were to comprise an active waveguide or resonator according tothe present invention, optical power transfer between the devices couldthen be controlled through active control of the modal index asdescribed in the preceding paragraph, typically using control signals ofsubstantially smaller magnitude than required by previously availabledevices. Optical signal power transfer from a fiber-optic or otherlow-index optical waveguide into an integrated on-chip optical device(typically high-index) may be greatly improved and/or activelycontrolled by employing waveguide and/or resonator structures accordingto the present invention. Optical losses within such an integratedon-chip device may be reduced. Waveguides and resonators according tothe present invention may be substantially modal-index-matched tooptical fiber or other low-index waveguides, may possess low opticalloss and/or high optical Q-factors, and may be controlled by relativelysmall control signals. Waveguides according to the present invention maybe used for phase modulation in interferometric optical devices (such asa Mach-Zender interferometer modulator, for example) using smallercontrol signals than required by previously available devices.

[0194] A suitable multi-layer reflector (MLR) according to the presentinvention preferably includes a periodic, partially periodic,multi-periodic, quasi-periodic, and/or similar multi-layer dielectricstack. A MLR stack preferably includes layers of varying index(typically alternately increasing and decreasing index; oftenalternating layers of a higher-index material and a lower-indexmaterial) and exhibits wavelength-dependent optical properties.Graded-index materials may also be employed. A distributed Braggreflector (DBR) may serve as a preferred MLR according to the presentinvention and is shown and described in exemplary embodiments disclosedherein. However, other types of multi-layer-reflector structures may beemployed while remaining within the scope of inventive conceptsdisclosed and/or claimed herein.

[0195] A distributed Bragg reflector (DBR) preferably includesalternating quarter-wave (λ/4) layers of dielectric materials having asufficiently large material refractive index differential (typicallyexpressed as Δn/n_(avg)), typically greater than about 8%, preferablygreater than about 15%, most preferably greater than about 60%.Determination of the quarter-wave thickness depends on the designwavelength and the material index of the layer at the design wavelength,and typically a range of layer thicknesses will function suitably at agiven design wavelength. Fabrication techniques for the materials usedmust enable sufficiently precise growth or deposition of substantiallyuniform layers of material, typically with nanometer-scale precision.Such fabrication techniques often require use of materials (oftensemi-conductors, particularly III-V semiconductors and/or alloys,quantum wells, multi-quantum wells, super-lattices, and/or oxidationproducts thereof; other suitable materials may be equivalently employed)with crystalline lattice parameters sufficiently similar to allowdeposition of layers of the different materials on each other withoutsubstantial generation of strain and/or defects in the materials. Growthor deposition may also involve amorphous materials. Preferred techniquesinclude as examples crystalline growth or re-growth, amorphous growth orre-growth, vapor deposition, chemical vapor deposition, epitaxialdeposition, beam deposition, beam-assisted and/or beam-enhanceddeposition (beams may include optical, electron, ion, plasma, neutral,radical, and so forth), sputter deposition, plasma and/or ion beamdeposition; other suitable techniques may be equivalently employed. Theuse of III-V semi-conductors and/or alloys thereof for implementation ofthe present invention enables: use of technologically mature deposition,material processing, and other fabrication techniques; attainment ofdesirable optical properties for waveguide/resonator devices in thewavelength region(s) of interest (including a controllable refractiveindex via electro-active and/or non-linear-optical properties);integration of the optical device(s) onto a substrate along with controlelements therefor and electrical and/or optical connections thereto;integration of the optical device(s) onto a substrate along withIII-V-based light sources and/or detectors. Oxidation of III-Vsemiconductors and/or alloys also yields substantially lower-indexoxides of high optical quality, enabling fabrication ofhigh-index-contrast MLR stacks and high-index-contrast lateralconfinement of optical modes therein. All of these considerations limit,however, the particular combinations of materials and fabricationtechniques that may be employed for a device suitable for a givenapplication, which will be described in detail hereinbelow.

[0196] A general description of fabrication of MLR waveguides andresonators and general considerations dictating choices for materialsfollows. A vertical layer sequence may typically be constructed first(i.e. “vertical fabrication”) on one or more suitable substrates. Thevertical fabrication may proceed as a single sequence of layerdepositions on a single substrate to achieve the desired multi-layerstructure (referred to hereinafter as “single-substrate verticalfabrication”). Alternatively, the vertical fabrication may proceed asmultiple sequences of layer depositions on multiple substrates, withwafer-bonding and substrate etching techniques employed to form thesingle desired multi-layer structure on a single substrate (referred tohereinafter as “multi-substrate vertical fabrication” or “wafer-bondingvertical fabrication”). It should be noted that “wafer-bonding” shallgenerally encompass any technique suitable for bringing twosubstantially planar materials into substantially intimate contactsubstantially free of voids therebetween and establishing a bondtherebetween. In addition to bringing the two surfaces into contact,such techniques may further involve elevated temperature and or pressurefor periods of time in order to bond the materials together.Single-substrate fabrication may be employed when all layer materials tobe used are sufficiently compatible in their lattice properties to forma sufficiently low-strain and defect-free multi-layer structure by layerdeposition. When insufficiently compatible materials are used,multi-substrate fabrication may be employed to produce a sufficientlylow-strain and defect-free multi-layer structures, which aresubsequently wafer-bonded or otherwise assembled together, perhaps usingpolymer-based or other adhesive. Multi-substrate vertical fabricationtherefore permits a much wider range of material combinations to beemployed, at the expense of more complex fabrication procedures. Thewider range of material combinations may enable, for example, use ofmaterials optimized for forming MLR stacks of high optical quality inconjunction with electro-active and/or non-linear optical materialsoptimized for the design wavelength but that may not belattice-compatible with the MLR materials. The ability to use a widerrange of materials enables tailoring of the electro-optic properties ofthe waveguide and the dispersive properties of the MLR stack(s) forspecific performance characteristics of an optical device employing thewaveguide. It should be noted that multi-substrate fabrication may bedesirable and employed with materials that might also be suitable forsingle-substrate fabrication.

[0197] Vertical fabrication is preferably followed by spatiallyselective processing of portions of some or all layers of themulti-layer structure (i.e., “horizontal fabrication”), producing awaveguide or resonator of the desired size, shape, and topology.Horizontal fabrication may include removal of multi-layer material toleave protruding ridge, protruding mesa, stepped, and/or recessedstructure(s); such structures may be shallow structures involving onlythe few top layers of the multi-layer structure, or may be deepstructures involving most or all of the layers of the multi-layerstructure. Horizontal fabrication may include deposition of lateralcoatings on such a protruding, stepped, or recessed structures,including but not limited to lateral metallic coatings (opticallyreflective and/or electrical contact layers), lateral dielectriccoatings, lateral multi-layer reflectors or distributed Braggreflectors, or other lateral coating. Horizontal fabrication may alsoinclude chemical conversion and/or modification of some or all layers ofthe MLR or DBR, either after forming the protruding, stepped, orrecessed structure(s), and/or for forming a buried structure. Theconversion/modification may involve all, some, or none of eachindividual layer of the multi-layer structure, and may proceed from oneor both sides of a protruding and/or recessed structure. Horizontalfabrication may include spatially-selective modification of lateralportions of the waveguide structure for lateral confinement of a guidedoptical mode. This may include providing lateral cladding or MLR layersby spatially-selective chemical, physical, or optical modification ofthe multi-layer structure by material deposition or re-deposition,material growth or re-growth, photolithography, beam lithography,doping, implantation, densification, etching, or other suitabletechniques including other material growth/deposition/processingtechniques recited herein.

[0198] In addition to MLR layers, waveguide core layers, electro-activelayers, and/or non-linear optical layers, additional layers may beincluded as physical spacers and/or insulators (i.e., buffer layers), asprotective overlayers (i.e., cladding layers), as conductive electricalcontacts (i.e., contact layers; metallic and/or semi-conductor), and/orlayers for enabling control of the fabrication processes (i.e.,etch-stop layers). A buffer layer may function as an electrical buffer(moving a portion of the waveguide structure beyond the localizedinfluence of a contact layer, for example) and/or as an optical buffer(maintaining a portion of a guided optical mode away from layers havingundesirable optical properties, adjust the thickness of a particularlayer, or other purposes). Individual layers may fulfill more than oneof these functions. For many of the structures disclosed herein, thewaveguide layer structure may preferably include top and bottomelectrical contact layers with one or more electro-active layerstherebetween. Application of a voltage across these contact layersproduces an electric field substantially perpendicular to the layers ofthe waveguide (substantially vertical). This electric field causesvariation of the optical properties any electro-active layers present,and the dispersive properties of the MLR structure(s) of the waveguideresult in a substantial change in the modal index of a guided opticalmode (as described hereinabove). Other configurations may be employedfor the application of an electric field to the electro-optic layer(s),however, and substantially horizontal electric fields (transverse and/orlongitudinal) may be employed, for example, without departing frominventive concepts disclosed and/or claimed herein.

[0199] For a single-MLR device, a wafer may be grown including asuitable substrate, a bottom buffer/etch-stop layer (if desired orneeded), a doped bottom electrical contact layer (often delta-doped inthe case of III-V semiconductors and alloys), another buffer/etch-stoplayer (if desired or needed), alternating λ/4 layers of a pair ofmaterials comprising a DBR stack (either having sufficient indexcontrast to form a DBR, or which may be converted during subsequentprocessing to materials possessing such an index contrast; typicallybetween 3 and 10 or more pairs of layers may be employed), a topbuffer/etch-stop layer (if desired or needed), a top core layer (betweenλ/4 and λ/2), and a top cladding/etch-stop layer (if desired or needed).Electro-active and/or nonlinear optical properties for active control ofthe waveguide/resonator may be incorporated into this structure in avariety of ways, if desired or needed.

[0200] In a group of single-substrate fabrication processes forfabricating single-MLR devices, one or more of the λ/4 layers,buffer/etch-stop layers (if present), core layer, and/orcladding/etch-stop layer may comprise an electro-active ornon-linear-optical material. The flowchart of FIG. 15 and processdiagram of FIG. 16 illustrate a single-substrate fabrication procedurewherein the core layer 1604 comprises an electro-active ornon-linear-optical material. First, a doped electrical contact/etch-stoplayer 1620 (meaning that the contact layer may also function as anetch-stop layer, if desired) is deposited on substrate 1610 (if desiredor needed). Buffer/etch-stop layers (meaning these layers may functionas buffers and/or etch-stop layers) may optionally be deposited beforeand/or after deposition of contact layer 1620. In this and allsucceeding diagrams, optional buffer/etch-stop layers andcladding/etch-stop layers are omitted for clarity. A DBR stack 1602 ofabout 5 to about 20 alternating lower- and higher-index quarter-wavelayers is then deposited, with the topmost layer comprising alower-index layer. “Lower-index” and “higher-index” here describe thematerial indices of the layers as they will exist after all fabricationand processing are complete, as does the description “quarter-wave”. Forexample, the proper quarter-wave thickness for a particular layer is notnecessarily determined by the material index of the material deposited,but the material which eventually comprises the layer. In some casesthis will be the deposited material, but in other cases may be a newmaterial obtained from the deposited material through a chemicalconversion process during subsequent processing. Similarly, whether agiven layer is a lower-index or higher-index layer depends on the indexof the layer material after all fabrication and processing are complete.A higher-index deposited material may, for example, be converted to alower-index layer material during subsequent processing. A waveguidecore layer 1604 may then be deposited (after an optionalbuffer/etch-stop layer, if desired) comprising a higher-indexelectro-active or non-linear-optical material and having a layerthickness between about quarter-wave and about half-wave. Thedistinction between a quarter-wave core layer 1604 and the quarter-wavelayers of DBR 1602 is a somewhat artificial one. A top doped electricalcontact/etch-stop layer 1630 may then be deposited (if desired orneeded; preceded by an optional buffer/etch-stop layer if desired, andfollowed by an optional cladding/etch-stop layer if desired), completingthe vertical fabrication of this particular structure.

[0201] In the layer deposition scheme described hereinabove and in otherdeposition schemes described hereinbelow, it should be noted thatelectrical contact layers may only be required if electro-activelayer(s) are included in the multi-layer waveguide structure (typicallyfor active modal-index control). Such electrical contact layers and/orelectro-active layers may be omitted from waveguides incorporating oneor more non-linear-optic layers for active modal-index control or fromwaveguides employing passive modal-index matching. While top and bottomelectrical contact layers may preferably be located near the top andbottom, respectively, of the multi-layer structure, this need not alwaysbe the case. Top and bottom electrical contact layers may be placed inany suitable position within the multi-layer structure with theelectro-active layer(s) therebetween. Electrical contact layers maypreferably be oriented substantially parallel to the other layers in themulti-layer structure, so that an electric field applied through thecontact layers would be substantially perpendicular to the layers.Alternatively, electrical contacts may be applied laterally so that acontrol electric field would be applied substantially parallel to thelayers of the multi-layer structure. It should also be noted that whilethe layer deposition schemes recited herein describe deposition of DBRstacks, all of these deposition schemes may be generalized to includeany MLR structure, including periodic, partially periodic,multi-periodic, quasi-periodic, or other varying-index MLR structure,while remaining within the scope of inventive concepts disclosed and/orclaimed herein.

[0202] The flowchart of FIG. 17 and process diagram of FIG. 18illustrate a single-substrate vertical fabrication procedure wherein alayer 1808 of electro-active or non-linear-optical material is depositedseparately from core layer 1804. First, a doped electricalcontact/etch-stop layer 1820 is deposited on substrate 1810.Buffer/etch-stop layers may optionally be deposited before and/or afterdeposition of contact layer 1820, and are not shown. A DBR stack 1802 ofabout 5 to about 20 alternating lower- and higher-index quarter-wavelayers is then deposited, with the topmost layer comprising alower-index layer. A waveguide core layer 1804 may then be deposited(after an optional buffer/etch-stop layer, if desired) comprising ahigher-index material and having a layer thickness between aboutquarter-wave and about half-wave. Electro-active or non-linear-opticalmaterial layer 1808 may then be deposited (preceded by an optionalbuffer/etch-stop layer if desired). A top doped electricalcontact/etch-stop layer 1830 may then be deposited (preceded by anoptional buffer/etch-stop layer if desired, and followed by an optionalcladding/etch-stop layer if desired), completing the verticalfabrication of this particular structure. Alternatively, the order ofdeposition of the core layer and electro-active or non-linear-opticallayer may be reversed.

[0203] The flowchart of FIG. 19 and process diagram of FIG. 20illustrate a single-substrate vertical fabrication procedure wherein amaterial comprising at least one layer of DBR stack 2002 is anelectro-active or non-linear-optical material. First, a doped electricalcontact/etch-stop layer 2020 is deposited on substrate 2010.Buffer/etch-stop layers may optionally be deposited before and/or afterdeposition of contact layer 2020, and are not shown. A DBR stack 2002 ofabout 5 to about 20 alternating lower- and higher-index quarter-wavelayers is then deposited, with the topmost layer comprising alower-index layer. One or more of the DBR layers (lower-index material,higher-index material, or both DBR materials) may comprise a layer ofelectro-optic active or non-linear-optical material. A waveguide corelayer 2004 may then be deposited (after an optional buffer/etch-stoplayer, if desired) comprising a higher-index material and having a layerthickness between about quarter-wave and about half-wave. A top dopedelectrical contact/etch-stop layer 2030 may then be deposited (precededby an optional buffer/etch-stop layer if desired, and followed by anoptional cladding/etch-stop layer if desired), completing the verticalfabrication of this particular structure. Direct incorporation ofelectro-active or non-linear-optical material into DBR 2002 enablessimplification of the vertical fabrication of an active waveguideaccording to the present invention.

[0204] In each of the vertical layer structures of FIGS. 15-20fabricated using single-substrate vertical fabrication procedures, thelattice properties of the electro-active or non-linear-optical materialmust be substantially compatible with those of the λ/4 layers (DBRlayers), core layer, the upper electrical contact layer, and/or uppercladding layer (if present), in order to form a sufficiently low-strainand/or defect-free structure. Application of a control voltage acrossthe top and bottom contact layers (vertical control electric field)enables active control of the optical properties of an electro-activelayer, in turn enabling control of a modal index of an optical modesupported by the ultimate waveguide structure. Alternatively, the topand bottom electrical contact layers may be omitted and replaced withlateral electrical contacts during subsequent horizontal fabrication,enabling application of a horizontal control electric field. Applicationof a control optical signal enables active control of the opticalproperties of a non-linear optical layer, in turn enabling control of amodal index of an optical mode supported by the ultimate waveguidestructure.

[0205] If the lattice properties of the DBR materials and theelectro-active or non-linear-optical material are not substantiallycompatible, a group of multi-substrate vertical fabrication processesmay be employed to construct surface-guided waveguides. The flowchart ofFIG. 21 and process diagram of FIG. 22 illustrate a two-substratevertical fabrication procedure wherein two separate substrates may beutilized for deposition of material layers and the resulting structuresmay be wafer-bonded together, eliminating the need for substantiallycompatible lattice properties. First, a doped electricalcontact/etch-stop layer 2220 is deposited on a first substrate 2210.Buffer/etch-stop layers may optionally be deposited before and/or afterdeposition of contact layer 2220, and are not shown. A DBR stack 2202 ofabout 5 to about 20 alternating lower- and higher-index quarter-wavelayers is then deposited, with the topmost layer comprising alower-index layer. A waveguide core layer 2204 may then be deposited(after an optional buffer/etch-stop layer, if desired) comprising ahigher-index material and having a layer thickness between aboutquarter-wave and about half-wave. A second doped electricalcontact/etch-stop layer 2230 is deposited on a second substrate 2240,which need not be lattice-compatible with substrate 2210 or any of thelayers deposited thereon. Buffer/etch-stop layers may optionally bedeposited before and/or after deposition of contact layer 2230, and arenot shown. Electro-active or non-linear-optical material layer 2208 maythen be deposited (followed by an optional buffer/etch-stop layer ifdesired). The second substrate is then inverted, and wafer bonded to thetopmost layer on the first substrate using any suitable wafer-bondingtechnique. In this way materials having lattice propertiesinsufficiently compatible to allow direct deposition of a singlemulti-layer structure may nevertheless be incorporated into such astructure. After wafer-bonding, the second substrate 2240 may be etchedaway, completing the vertical fabrication of this particular structure.

[0206] Several related alternative two-substrate vertical fabricationprocedures are illustrated in FIGS. 23, 24, 25, and 26. In FIGS. 23 and24, a doped electrical contact/etch-stop layer 2420 is first depositedon a first substrate 2410. Buffer/etch-stop layers may optionally bedeposited before and/or after deposition of contact layer 2420, and arenot shown. A DBR stack 2402 of about 5 to about 20 alternating lower-and higher-index quarter-wave layers is then deposited, with the topmostlayer comprising a lower-index layer, after which an optionalbuffer/etch-stop layer may be deposited, if desired. A second dopedelectrical contact/etch-stop layer 2430 is deposited on a secondsubstrate 2240, which need not be lattice-compatible with substrate 2410or any of the layers deposited thereon. Buffer/etch-stop layers mayoptionally be deposited before and/or after deposition of contact layer2430, and are not shown. A waveguide core layer 2404 may then bedeposited (followed by an optional buffer/etch-stop layer, if desired)comprising a higher-index material and having a layer thickness betweenabout quarter-wave and about half-wave. Electro-active ornon-linear-optical material layer 2408 may then be deposited (followedby an optional buffer/etch-stop layer if desired). The second substrateis then inverted, and wafer bonded to the topmost layer on the firstsubstrate using any suitable wafer-bonding technique. Afterwafer-bonding, the second substrate 2440 may be etched away, completingthe vertical fabrication of this particular structure. The order ofdeposition of the core layer and electro-active or non-linear-opticallayer may be reversed. FIGS. 25 and 26 illustrate an analogousfabrication procedure involving a first substrate 2610 with contactlayer 2620 and DBR 2602, and a second substrate 2640 with contact layer2630 and electro-active or non-linear-optical core layer 2604.Wafer-bonding the topmost layers of the two substrates and then etchingaway substrate 2640 yields the desired layer structure.

[0207] Whichever class of procedures is used (single-substrate, ortwo-substrate), the resulting vertical structure comprises a single DBRstack for surface guiding an optical mode and incorporates at least oneelectro-active or non-linear-optical layer, with contact layers aboveand below (if needed). Application of a control voltage across the topand bottom electrical contact layers (vertical control electric field)enables active control of the optical properties of the electro-activelayer. In either group of surface-guided structures, the top and bottomelectrical contact layers may be omitted and replaced with lateralelectrical contacts during subsequent horizontal fabrication, enablingapplication of a horizontal control electric field. Application of acontrol optical signal enables active control of the optical propertiesof a non-linear optical layer.

[0208] For devices incorporating two MLR structures confining an opticalmode therebetween (i.e., dual- or partial-dual-DBR devices), similarsingle- and multi-substrate vertical fabrication methods may beemployed. A wafer may be grown comprising a suitable substrate, a bottombuffer or cladding layer (if desired or needed), a doped bottomelectrical contact layer (often delta-doped in the case of III-Vsemiconductors and alloys), another buffer or cladding layer (if desiredor needed), and a first set of alternating λ/4 layers of a pair ofmaterials comprising a bottom DBR stack (either having sufficient indexcontrast to form a DBR, or which may be converted during subsequentprocessing to materials possessing such an index contrast; typicallybetween 3 and 10 or more pairs of layers may be employed). A λ/2waveguide layer (i.e., core layer), a top DBR stack of alternating λ/4layers, and the electro-active or non-linear-optical properties requiredfor active control of the waveguide/resonator may be incorporated intothis structure in a variety of ways.

[0209] The flow diagram of FIG. 27 and fabrication process diagram ofFIG. 28 show a single-substrate vertical fabrication process wherein abottom contact layer 2820 is deposited on a substrate 2810 (preceded andor followed by buffer/etch-stop layers if desired or needed; not shown).After deposition of bottom DBR stack 2802 (and a buffer/etch-stop layer,if desired), half-wave waveguide core layer 2804 may be depositeddirectly over the bottom DBR stack 2802 (followed by a buffer/etch-stoplayer, if desired). An electro-active or non-linear-optical layer 2808may be deposited next (followed by a buffer/etch-stop layer, ifdesired). The order of deposition of the core layer and electro-activeor non-linear-optical layer may be inverted. A second set of alternatingλ/4 layers (either the same pair of materials as used for bottom DBRstack 2802, or a suitable alternative pair of substantiallylattice-compatible materials) may then be deposited over electro-activeor non-linear-optical layer 2808 to form top DBR stack 2806. DBR stack2806 may typically comprise from 1 to about 20 layers of alternatinglower- and higher-index quarter-wave layers with a lower-indexbottom-most layer, the number of layers being employed depending on theevanescent properties sought for the waveguide ultimately produced.Fewer layers in top DBR stack 2806 results in a larger evanescentportion of a supported optical mode extending upward from the waveguidebeyond upper DBR stack 2806. A top electrical contact/etch-stop layer2830 (preceded and/or followed by buffer/etch-stop layer(s) if desired)may then be deposited, substantially completing the vertical fabricationof the double DBR layer structure.

[0210] Instead of a separate electro-active or non-linear-optical layer2808, the single-substrate fabrication procedure of FIGS. 29 and 30 maybe followed, comprising deposition on substrate 3010 of contact layer3020, bottom DBR stack 3002, core layer 3004 comprising a half-wavelayer of electro-active or non-linear-optical material, top DBR stack3006, and top contact layer 3030. Alternatively, as illustrated in FIGS.31, 32, 33, and 34, one or more layers of the bottom DBR 3402 and/or topDBR 3406 may comprise a layer of electro-active or non-linear-opticalmaterial. In any of these single-substrate vertical fabricationprocedures the lattice properties of the electro-optic layer materialmust be substantially compatible with those of the λ/4 layers, waveguidelayer, and or contact layers in order to form a sufficiently low-strainand/or defect-free structure. Application of a control voltage acrossthe top and bottom contact layers (vertical control electric field)enables active control of the optical properties of the electro-activelayer, wherever it is located. Application of a control optical signalenables active control of the optical properties of a non-linear opticallayer.

[0211] If the lattice properties of the various layer materials are notsufficiently compatible to enable vertical fabrication of dual- orpartial-dual-DBR structures as a single growth sequence on a singlesubstrate as described above, multi-substrate vertical fabricationtechniques may be employed to enable incorporation oflattice-incompatible materials into dual-or partial-dual-DBR waveguides.In each of the fabrication procedures illustrated in FIGS. 35, 36, 37,38, 39, and 40 three substrates are employed. A bottom contact andbottom DBR stack are grown on a first substrate, an electro-active ornon-linear-optical is deposited on a second substrate (alone, along witha separate core layer, or as the core layer), and a top contact and topDBR stack are grown on a third substrate. If a waveguide layer is notdeposited on the second substrate, it may be deposited on either of theother substrates. The second substrate (with the electro-active ornon-linear-optical layer) is inverted and wafer-bonded to the firstsubstrate (with the bottom DBR stack), and the second substrate isetched away. The third substrate (with the top DBR stack) is theninverted and wafer-bonded to the remaining layers of the secondsubstrate. The third substrate is removed, substantially completing thevertical fabrication of the dual-DBR layer structure. With theseprocedures the lattice properties of the electro-active ornon-linear-optical material need not be compatible with those of eitherset of λ/4 layers. Application of a control voltage across the top andbottom electrical contact layers (vertical control electric field)enables active control of the optical properties of the electro-activeor non-linear-optical layer. In either group of dual-DBR structures(single-substrate or multi-substrate vertical fabrication), the top andbottom electrical contact layers may be omitted and replaced withlateral electrical contacts during subsequent horizontal fabrication,enabling application of a horizontal control electric field. Applicationof a control optical signal enables active control of the opticalproperties of a non-linear optical layer.

[0212] Whichever of the above described vertical fabrication methods isemployed (single- or multi-substrate), and whether a single- or dual-DBRstructure is employed, the resulting multi-layer structure must befurther processed (by so-called “horizontal fabrication”) to producelaterally-confined waveguides and resonators according to the presentinvention. Such waveguides and resonators may take the form of aprotruding ridge-like structure, a protruding mesa-like structure, astepped structure, a recessed structure, and/or a buried structure onthe substrate. Alternatively, such waveguides and resonators may takethe form a structures of varying density, chemical composition,refractive index, or other physical property. These structures may takethe form of linear segments, arcuate segments, or other open waveguidestructures, or may take the form of rings, circles, ovals, racetracks,ellipses, polygons, or other closed waveguide (i.e., resonator)structures. Other topologies may be employed for more specializedintegrated optical devices, such as Mach-Zender interferometers,directional couplers or 2×2 switches, and the like (as in FIGS. 1 and 2,for example). Once a wafer has been produced according to any of thevertical fabrication methods described hereinabove (or other suitablyequivalent methods), any suitable spatially-selective lithographicpatterning and/or etching technique(s), or other functionally equivalentspatially-selective material processing techniques, may be employed tomodify portions of the multi-layer structure, thereby forming on thesubstrate structures (protruding, recessed, buried, chemically orphysically altered, etc) of the desired topology. Generic examples areshown schematically in FIGS. 41A through 43B using apatterned-mask/etching technique. Other suitable techniques, includingdirect lithographic techniques requiring no mask, optical lithographictechniques, deposition, assisted deposition, re-growth, re-deposition,and other techniques and/or processes described herein, for example, maybe equivalently employed.

[0213] In FIG. 41A, a substrate 4110 is shown with a multi-layerstructure 4160 thereon and a mask layer 4170. Mask 4170 may be depositedand spatially patterned by any suitable technique, including but notlimited to lithographic techniques. The spatial pattern of mask 4170 isdetermined by the size, shape, and topology desired for the waveguide orresonator to be produced, and in this example mask 4170 is configured toyield a simple linear waveguide segment 4100. The un-masked portions ofmulti-layer structure 4160 may be substantially completely removed byany suitable technique, including but not limited to dry and/or wetetching techniques. After removal of the un-masked portions ofmulti-layer 4160, mask 4170 may be removed, leaving waveguide 4100 onsubstrate 4110. Analogous procedures are illustrated in FIGS. 42A and43A involving substrate 4210/4310, multi-layer 4260/4360, and mask4270/4370 yielding resonator 4200/4300. It should be noted that asmulti-layer 4160/4260/4360 is removed, laterally exposed portions of themulti-layer may come under attack during some etching procedures, andthe size and shape of the resulting waveguide 4100/4200/4300 may bedifferent than the initial size and shape of mask 4170/4270/4370(slightly smaller and/or narrower, for example). Depending on theprecise nature and sequence of layers of multi-layer 4160/4260/4360, andthe presence/absence of etch-stop layers therein, more complex, steppedstructures may be obtained. This may be advantageous for leavingportions of contact layers exposed for later electrical connection to acontrol signal source, for example, or for producing localized contactlayers for applying localized control signals, or for producing awaveguide/resonator 4100/4200/4300 having optical properties that varyalong its length, or for other purposes. It may be desirable to performa series of deposition and/or wafer-bonding steps alternating withspatially-selective etch steps (i.e., intermingling the “verticalfabrication” and the “horizontal fabrication”), to obtain complexwaveguide/resonator structures.

[0214] The multi-layer structure may be deep-etched (i.e., most or allof the way through the multi-layer structure down toward the substrate;FIGS. 41A, 42A, and 43A). In this case modes supported by the waveguidemay be strongly laterally confined by the relatively large indexcontrast at the sides of the waveguide. Alternatively, a relativelyshallow etch may be employed (FIGS. 41B, 42B, and 43B), removingmaterial from only the top few layers (or even a portion of only onelayer). The lateral optical confinement provided by such ashallow-etched waveguide is correspondingly weaker than that provided bya deep-etched waveguide. This may provide desirable optical performancecharacteristic for the resulting waveguide, such as support of fewertransverse optical modes than a deep-etched waveguide or reduced opticalloss induced by etched surfaces, for example. The two sides ofwaveguide/resonator 4100/4200/4300 may each have material removed to thesame depth, or to differing depths, as desired for fabricating specificdevices.

[0215] The index contrast between the sides of the waveguide structureand the surrounding lower-index medium (examples given hereinabove) mayprovide lateral confinement of an optical mode supported by thewaveguide/resonator structure (whether single-, dual-, orpartial-dual-MLR). However, the etched side surfaces will often havesubstantial roughness and/or numerous defects due to the etchingprocess, degrading the propagation characteristics and/or mode qualityof a supported optical mode and/or degrading the Q-factor of an opticalresonator. Also, the relatively large index contrast may give rise toundesirable multi-transverse-mode behavior. It may therefore bedesirable to provide some or all of the layers of the multi-layerstructure (either single- or dual-MLR structures) with laterallower-index portions having a refractive index intermediate between thehigher-index of the medial portion of the respective layer and the indexof the surrounding medium (usually air, but possibly some other ambientover-layer). This may provide several advantages, including: 1) asupported optical mode may be confined by the index contrast between thehigher-index medial portion and the lower-index lateral portions of thelayers, thereby reducing and/or limiting the number of transverseoptical modes supported by the waveguide and simplifying design andoperation of devices incorporating the waveguide; 2) since it is guidedby the higher-index medial portion of the waveguide, the supportedoptical mode may interact less with the etched lateral surfaces of thewaveguide, thereby limiting the degradation produced by roughness and/ordefects at the etched surface; 3) the processing required to provided alayer with lateral lower-index portions may also reduce the roughnessand/or defect density at the etched lateral surface of the waveguide. Itmay be desirable to extend these lateral intermediate-index portionsacross the entire width of some layers of the multi-layer waveguidestructure, to provide enhanced index contrast in the MLR stack(s).Greater index contrast in the MLR stacks may result in better verticalguiding/confinement of a supported optical mode using fewer layers.

[0216] Lateral lower-index portions may be readily provided inmulti-layer waveguide structures (both single- and dual-MLR) fabricatedusing III-V semi-conductors and/or alloys, quantum wells, multi-quantumwells, and/or super-lattices thereof. These materials typically haveindices between about 2.9 (AlAs) and about 3.4 (GaAs), withAl_(x)Ga_(1−x)As alloys falling between these extremes. III-V materialshaving substantial aluminum content may be readily oxidized to aluminumoxides (Al_(x)O_(y)), having indices between about 1.5 and about 1.7.This may be exploited, for example, by fabricating a MLR stack fromalternating layers of GaAs 4420 and high-aluminum AlGaAs 4430(Al_(0.98)Ga_(0.02)As), as shown in FIG. 44. After vertical andhorizontal fabrication to produce a protruding DBR waveguide structure4400, the wafer may be oxidized by (for example) bubbling N₂ throughwater at 85° C. and then passing the N₂ over the waveguide in a furnaceat 425° C. The aluminum-containing layers 4430 are preferentiallyoxidized at a rate of about 1 μm/min (depending on layer thickness,aluminum content, and so forth), and the oxidation proceeds from theexposed edge of each aluminum-containing layer 4430 inward (processreferred to hereinafter as “lateral oxidation”). Depending on theoxidation time, layer thickness, layer aluminum content, and so forth,the oxidized layer may have lateral aluminum oxide portions 4432surrounding a central AlGaAs portion 4434. If the oxidation is permittedto proceed long enough, the entire layer may be converted to an aluminumoxide layer 4436, providing a much higher material index contrast MLR(about 1.5 to 3.4) than the original MLR layer structure (about 2.9 to3.4). It should be noted that lateral oxidation or other lateralchemical modification of any MLR layers may proceed form one or bothsides of a waveguide structure.

[0217] It should be noted that the desired thickness of layers 4430(AlGaAs) depends on whether the oxidation is used to produce lateraloxide portions 4432 or full oxide layers 4436. If lateral oxide portions4432 are to be produced, then the desired quarter-wave thickness formedial portions 4434 is determined based on the design wavelength andmaterial index for the AlGaAs alloy being used, and this thickness isprovided during vertical fabrication of the wafer from which MLR 4400 ismade. If full aluminum oxide layers 4436 are to be produced, the desiredquarter-wave thickness is determined based on the design wavelength andthe material index of the aluminum oxide. This oxide-index-basedthickness is provided for the AlGaAs layers 4430 during verticalfabrication of the wafer. As an example, at a design wavelength of about1500 nm, AlGaAs layers 4430 should be about 130 nm thick to yieldquarter-wave medial AlGaAs portions 4434, but should be about 270 nmthick to yield quarter-wave aluminum oxide layers 4436.

[0218]FIG. 45 shows a further refinement of the lateral oxidation schemeoutlined above, wherein the Al concentration of AlGaAs layers 4430varies, decreasing with each additional AlGaAs layer 4430 added duringvertical fabrication of the wafer. The lateral oxidation rate increaseswith increasing Al content, so that for a given oxidation time thevertically tapered MLR of FIG. 45 results, which may or may not includeone or more full oxide layers 4436. (In general, the lateral oxidationrate depends on the thickness of the layer, the chemical composition ofthe surrounding layers, and the Al content. However, in the presentcircumstances, only the Al content can be independently varied.) FIGS.46 and 47 show dual-MLR structures analogous to FIGS. 44 and 45,respectively. The transverse waveguide geometries shown in FIGS. 44through 47 each have desirable optical characteristics. The medialAlGaAs/GaAs MLR's of FIGS. 43-47 have the advantage of horizontallyconfining and guiding a supported optical mode away from lateral edgesof waveguide 4300 and any roughness and/or defects thereon. The higherindex contrast of the GaAs/Al_(x)O_(y) MLR's of FIGS. 44 and 46 enablesvertical confinement and guiding of a supported optical mode using fewerMLR layers. The vertically tapered AlGaAs/GaAs MLR's of FIGS. 45 and 47may better serve to horizontally confine and guide the optical mode.

[0219] Both improved horizontal confinement (away from potentially pooroptical quality lateral waveguide surfaces), and vertical confinementwith fewer layers of a higher contrast MLR, may be achievedsimultaneously in a waveguide structure. As in the process of FIGS. 45and 47, differential oxidation rates may be exploited to achieve variousdesired transverse layer geometries. As before, a given layer thicknessprovided during vertical fabrication of a wafer is determined by thedesign wavelength and the index of the material that eventuallycomprises the layer, not necessarily the index of the materialdeposited. In general, oxidation rates of III-V semi-conductors increasewith increasing aluminum content. A MLR wafer may be fabricated fromalternating layers of Al_(0.98)Ga_(0.02)As 4530 and Al_(0.96)Ga_(0.04)As4520 (FIG. 48). Follo horizontal processing to form a protruding ridgestructure 4500, lateral oxidation may be initiated and permitted toproceed until each entire Al_(0.98)Ga_(0.02)As layer 4530 has beenconverted to a substantially complete aluminum oxide layer 4536, while amedial portion 4524 of each Al_(0.96)Ga_(0.04)As layer 4520 remains,flanked by lateral aluminum oxide portions 4522. The resulting waveguidestructure then comprises a high-index-contrast central DBR portion(Al_(0.96)Ga_(0.04)As/Al_(x)O_(y); about 2.9 to about 1.5) surroundedlaterally by a lower-index medium (Al_(x)O_(y); about 1.5). As theoxidation of layers 4520 and 4530 progresses, medial portion 4524 maycome under attack and begin to oxidize from above and below. Someexperimentation may be required to determine, for a given set of layercompositions and oxidation conditions, the appropriate thicknesses forlayers 4520 and 4530 to achieve the desired thicknesses for layers 4536and 4524. Other material combinations may be amenable to a schemesimilar to that of FIG. 48. Layers 4520 and 4530 may comprisequarter-wave layers of AlAs/InAs superlattice material, for example,with the AlAs fraction of layers 4530 being higher than the AlAsfraction of layers 4520. The after horizontal fabrication to form ridgewaveguide 4500, lateral oxidation may be employed to produce Al_(x)O_(y)layers 4536 (from substantially complete oxidation of layers 4530)alternating with layers having AlAs/InAs superlattice medial portion4524 and lateral Al_(x)O_(y) portions 4522. During vertical fabricationof the wafer, the thicknesses provided for layers 4520 and 4530 arechosen to yield the desired thicknesses for layers 4536 and 4524. Forboth of these schemes (and functionally equivalent schemes using othermaterial combinations), the lower-index aluminum oxide lateral portions4522 of the resulting DBR waveguide laterally confine a supportedoptical mode away from the lateral surfaces of waveguide 4500, while thehigh index contrast of medial AlAs/InAs portions 4524 and aluminum oxidelayers 4536 provide vertical confinement with fewer DBR layers.

[0220] It may be desirable to provide asymmetric lateral lower-indexportions of layers of a waveguide. This may be the case, for example,when a dual-DBR waveguide will be used for transverse-coupling toanother optical element on only one side of the waveguide. As shown inFIGS. 49 and 50, wider lower-index lateral portions 4622 may be providedon the non-coupling side of the waveguide 4600, thereby reducing orsubstantially eliminating any evanescent portion of a waveguide opticalmode extending beyond the non-coupling side of the waveguide. Narrowerlateral portions 4624 may be provided on the coupling side of thewaveguide 4600, thereby enabling an evanescent portion of an opticalmode guided by medial higher-index medial portions 4620 to extend beyondthe coupling side of waveguide 4600. The differing widths may beachieved by masking the coupling side of waveguide 4600 during a portionof the lateral oxidation process, reducing the extent to which theoxidation progresses across the layers from the coupling side ofwaveguide 4600.

[0221] It may be desirable to ensure that the lateral oxidation proceedsfrom one side of the waveguide only, so as to avoid material defectsthat may arise when counter-propagating oxidation fronts meet within awaveguide structure along a boundary layer or interface. A shallow etchmay be performed to provide lateral optical confinement for thewaveguide structure. A deeper etch may be done farther away (i.e., farenough so as to substantially eliminate interaction between thesupported optical mode and the deep-etched side surface). Lateraloxidation may then proceed from the deep-etched side across thewaveguide in only one direction, with no boundary layer or interfacebeing formed.

[0222] Specific examples of combinations of materials for fabricatingactive optical waveguides and resonators will now be discussed, alongwith advantages and limitations of each and wavelength ranges over whicheach might be suitable. Each combination may be used to fabricatesingle-, dual-, and/or partial dual MLR waveguides and resonators. Somematerial combinations may be suitable for both single- andmulti-substrate vertical fabrication, while others may only be suitablefor multi-substrate vertical fabrication. These examples may bepreferred combinations for particular uses and/or applications, butshould not be construed as limiting the scope of inventive conceptsdisclosed and/or claimed herein. Other combinations of materialssatisfying the general structural and functional criteria set forthherein may be employed without departing from inventive conceptsdisclosed and/or claimed herein.

[0223] Preferred electro-active (i.e., electro-absorptive and/orelectro-optic) or non-linear-optical materials for use in waveguides andresonators according to the present invention may be quantum-well (QW)and multi-quantum-well (MQW) materials. A quantum well typicallycomprises a thin layer of a lower bandgap material sandwiched betweenbarrier layers of a higher bandgap material. Thin is defined here assufficiently thin that the effective bandgap of the quantum well differsfrom the bulk bandgap of the lower bandgap material due to spatialconfinement effects, and typical quantum well layers may be on the orderof 1-20 nm thick. The optical properties of such quantum wells may betailored to a certain degree by the composition of the materials used(selected for bandgap, index, etc.), and may be actively controlled byapplication of a control electric field to a greater degree than bulksemiconductor materials. In particular, a quantum well may function asan electro-absorptive and/or an electro-optic material, via thequantum-confined Stark effect (QCSE), the Franz-Keldysh effect (FKE),the quantum-confined Franz-Keldysh effect (QCFKE), and/or othermechanisms. The use of multiple quantum well layers separated by barrierlayers (on the order of tens of nanometers thick) yields amulti-quantum-well material, wherein the electro-absorptive and/orelectro-optic properties of the individual quantum well layers areadditive. The quantum well and barrier layers are sufficiently thin thatfor optical wavelengths typically used in the waveguides and resonatorsof the present invention, the optical mode behaves substantially as ifthe multi-quantum-well layer were a uniform layer having an index equalto the average index of the layers of the multi-quantum well.

[0224] An exemplary waveguide or resonator according to the presentinvention may include a MLR stack(s) comprising alternating quarter-wavelayers of GaAs (index of about 3.5) and Al_(x)Ga_(1−x)As (index betweenabout 2.9 and 3.4). The aluminum fraction x may lie between about 0.8and 1.0, preferably between about 0.9 and 1.0, most preferably betweenabout 0.92 and about 0.98. The fabrication of high optical quality DBRstacks with this material combination is technologically mature and wellcharacterized. A core layer may preferably comprise GaAs, InGaAs, orAlGaAs, and doped GaAs, InGaAs, or AlGaAs may preferably be used forelectrical contact layers. Either p-type of n-type doping may be usedfor the contact layers, and delta doping may be preferred. Buffer,cladding, and/or etch-stop layers, if present, may preferably compriseGaAs, and the waveguide may preferably rest on a GaAs substrate (whichmay possibly be doped to serve as the bottom contact layer). Othersuitable materials may be equivalently employed for the substrate and/orthe core, buffer, cladding, and/or etch-stop layers.

[0225] For a single-substrate vertical fabrication of a single- ordual-MLR device using GaAa/AlGaAs MLR stack(s), a multi-quantum-wellmaterial comprising GaAs quantum well layers and Al_(x)Ga_(1−x)Asbarrier layers may be employed as the electro-active material. This MQWmaterial is lattice-compatible with the GaAs/AlGaAs MLR stack(s),thereby enabling single-substrate vertical fabrication. The wavelengthrange over which the useful electro-absorptive and/or electro-opticproperties of this MQW material may extend is from about 0.7 μm to about0.8 μm, which determines the possible design wavelengths for thewaveguide and the corresponding quarter-wave thicknesses for the MLRstack layers. The MQW material may comprise the entire core layer (FIGS.15-16 and 29-30), or may comprise a separate layer (FIGS. 17-18 and27-28). Waveguides of these compositions may be further processed bylateral oxidation of the AlGaAs layers, as shown in FIGS. 44-47 and 49,thereby providing lateral aluminum oxide portions having a lower index(about 1.5-1.7) than the medial AlGaAs portions and confining asupported optical mode away from the lateral edges of the waveguide.Permitting lateral oxidation to proceed until substantially completeoxidation of the AlGaAs MLR stack layers (FIGS. 44, 46 and 50) resultsin a higher index contrast GaAs/Al_(x)O_(y) MLR stack (about 3.4 toabout 1.5). In this and other cases where an entire quarter-wave layeris converted by lateral oxidation, the quarter-wave layer thickness forthe initial material deposited must be determined based on the index ofthe final material present after lateral processing (oxidation orotherwise).

[0226] For a single-substrate vertical fabrication of a single- ordual-MLR device using GaAa/AlGaAs MLR stack(s), a multi-quantum-wellmaterial comprising GaAs quantum well layers and Al_(x)Ga_(1−x)Asbarrier layers may be employed as the electro-active material in placeof one or more layers of a MLR stack. This MQW material islattice-compatible with the GaAs/AlGaAs MLR stack(s), thereby enablingsingle-substrate vertical fabrication. The wavelength range over whichthe useful electro-absorptive and/or electro-optic properties of thisMQW material may extend is from about 0.7 μm to about 0.8 μm, whichdetermines the possible design wavelengths for the waveguide and thecorresponding quarter-wave thicknesses for the MLR stack layers. The MQWmaterial may comprise one or more layers of the MLR stack(s) (FIGS.19-20 and 31-34). Waveguides of these compositions may be furtherprocessed by lateral oxidation of the AlGaAs and/or GaAs/AIGaAs MQWlayers, as shown in FIGS. 44-47 and 49, thereby providing lateralaluminum oxide portions having a lower index (about 1.5-1.7) than themedial AlGaAs and/or MQW portions and confining a supported optical modeaway from the lateral edges of the waveguide. Permitting lateraloxidation to proceed until substantially complete oxidation of some ofthe MLR stack layers (FIGS. 44, 46, and 50) results in a higher indexcontrast GaAs/Al_(x)O_(y) MLR stack (about 3.4 to about 1.5). In thisand other cases where an entire quarter-wave layer is converted bylateral oxidation, the quarter-wave layer thickness for the initialmaterial deposited must be determined based on the index of the finalmaterial present after lateral processing (oxidation or otherwise).

[0227] For a single-substrate vertical fabrication of a single- or adual-MLR device using GaAa/AlGaAs MLR stack(s), a multi-quantum-wellmaterial comprising GaAs or AlGaAs barrier layers and In_(x)Ga_(1−x)Asquantum well layers may be employed as the electro-active material. ThisMQW material is lattice-compatible with the GaAs/AlGaAs MLR stack(s),thereby enabling single-substrate vertical fabrication. The wavelengthrange over which the useful electro-absorptive and/or electro-opticproperties of this MQW material may extend is from about 0.9 μm to about1.1 μm, which determines the possible design wavelengths for thewaveguide and the corresponding quarter-wave thicknesses for the MLRstack layers. The MQW material may comprise the entire core layer (FIGS.15-16 and 29-30), or may comprise a separate layer (FIGS. 17-18 and27-28). Waveguides of this configuration may be further processed bylateral oxidation of the AlGaAs layers, as shown in FIGS. 44-47 and 49,thereby providing lateral aluminum oxide portions having a lower index(about 1.5-1.7) than the medial AlGaAs portions and confining asupported optical mode away from the lateral edges of the waveguide.Permitting lateral oxidation to proceed until substantially completeoxidation of the AlGaAs MLR stack layers (FIGS. 44, 46, and 50) resultsin a higher index contrast GaAs/Al_(x)O_(y) DBR stack (about 3.4 toabout 1.5). In this and other cases where an entire quarter-wave layeris converted by lateral oxidation, the quarter-wave layer thickness forthe initial material deposited must be determined based on the index ofthe final material present after lateral processing (oxidation orotherwise).

[0228] For a single-substrate vertical fabrication of a single- ordual-MLR device using GaAa/AlGaAs DBR stack(s), a multi-quantum-wellmaterial comprising GaAs or AlGaAs barrier layers andIn_(x)Ga_(1−x)As_(1−y)N_(y) quantum well layers may be employed as theelectro-active material. The fraction x may range between about 0.05 andabout 0.30, preferably between about 0.1 and about 0.3, and mostpreferably about 0.15. The fraction y may range between about 0.001 andabout 0.04, preferably about 0.02. This MQW material islattice-compatible with the GaAs/AlGaAs MLR stack(s), thereby enablingsingle-substrate vertical fabrication. The wavelength range over whichthe useful electro-absorptive and/or electro-optic properties of thisMQW material may extend is from about 1.1 μm to about 1.45 μm (at abouty=0.02) and may be extended with further development. This wavelengthrange determines the possible design wavelengths for the waveguide andthe corresponding quarter-wave thicknesses for the MLR stack layers. TheMQW material may comprise the entire core layer (FIGS. 15-16 and 29-30),or may comprise a separate layer (FIGS. 17-18 and 27-28). Waveguides ofthis configuration may be further processed by lateral oxidation of theAlGaAs layers, as shown in FIGS. 44-47 and 49, thereby providing lateralaluminum oxide portions having a lower index (about 1.5-1.7) than themedial AlGaAs portions and confining a supported optical mode away fromthe lateral edges of the waveguide. Permitting lateral oxidation toproceed until substantially complete oxidation of the AlGaAs MLR stacklayers (FIGS. 44, 46, and 50) results in a higher index contrastGaAs/Al_(x)O_(y) MLR stack (about 3.4 to about 1.5). In this and othercases where an entire quarter-wave layer is converted by lateraloxidation, the quarter-wave layer thickness for the initial materialdeposited must be determined based on the index of the final materialpresent after lateral processing (oxidation or otherwise).

[0229] A waveguide or resonator according to the present invention mayinclude a MLR stack(s) comprising alternating quarter-wave layers ofAl_(0.96)Ga_(0.04)As (index of about 2.9 to 3.0) and Al_(y)O_(z) (indexbetween about 1.5 and 1.7). The MLR stack layers deposited duringvertical fabrication (FIGS. 15-18 and 27-30) comprise alternating layersof Al_(0.96)Ga_(0.04)As (quarter-wave thickness based on an index ofabout 3.0) and Al_(0.98)Ga_(0.02)As (quarter-wave thickness based on anindex of about 1.6), for example. Other aluminum fractions may beequivalently employed, including AlAs, and the aluminum fraction of thelower-aluminum layers may vary with distance from the substrate,yielding a tapered waveguide structure. The electro-active layer maycomprise any of the MQW materials listed thus far (GaAs/AlGaAs,GaAs/InGaAs, GaAs/InGaAsN). Lateral oxidation of the waveguide proceedsmore rapidly in the AlGaAs MLR layers having the higher Al content. Thelateral oxidation is allowed to proceed just to completion in theAl_(0.98)Ga_(0.02)As MLR layers, thereby leaving medial portions ofAl_(0.96)Ga_(0.04)As between lateral Al_(x)O_(y) portions in theAl_(0.96)Ga_(0.04)As layers (FIGS. 48 and 50). The resulting MLR stackcomprises low-index quarter-wave aluminum oxide layers alternating withlayers having a high-index quarter-wave Al_(0.96)Ga_(0.04)As medialportion surrounded by low-index aluminum oxide lateral portions. A corelayer may preferably comprise one of the electro-active MQW materials,GaAs, or AlGaAs, and doped GaAs or InGaAs may preferably be used forelectrical contact layers. Either p-type of n-type doping may be usedfor the contact layers, and delta doping may be preferred. Buffer,cladding, and/or etch-stop layers, if present, may preferably compriseGaAs or AlGaAs, and the waveguide may rest on a GaAs or AlGaAssubstrate. Other suitable materials may be equivalently employed for thesubstrate and/or the core, buffer, cladding, and/or etch-stop layers.

[0230] For operation in the 1.2 μm to 1.7 μm region, InGaAsP MQWmaterial grown on an InP substrate is the best characterized and mosttechnologically mature material available for use as an electro-opticand/or electro-absorptive layer. The bulk bandgap of the InGaAsPmaterial may be varied over this wavelength range by varying thestoichiometry. Quantum well layers about 10 nm thick with a 1.6 μm bulkbandgap separated by barrier layers about 20 nm thick with a 1.2 μm bulkbandgap may provide desirable electro-optic and/or electro-absorptivebehavior at an operating wavelength of about 1.5 μm, for example. Otherbandgaps and/or layer thicknesses may be equivalently employed.Unfortunately, the lattice properties of InGaAsP are not sufficientlycompatible with those of the GaAs/AlGaAs system to enablesingle-substrate vertical fabrication of sufficiently low-strain and/ordefect-free waveguide structures. Multi-substrate vertical fabricationmay be employed, however, to produce such structures, as illustrate inFIGS. 21-26 and 35-40. The MLR stack(s) (GaAs/AlGaAs, GaAs/Al_(x)O_(y),or AlGaAs/Al_(x)O_(y)) may be deposited onto GaAs or equivalentsubstrate(s), for example, while the InGaAsP MQW may be deposited ontoan InP or equivalent substrate. The InGaAsP MQW may be wafer-bonded overthe MLR, and the InP substrate may then be etched away, yielding asingle-MLR structure. A second MLR may be wafer-bonded over the MQWlayer and the corresponding GaAs substrate etched away, yielding adual-MLR structure. In this way the desired wavelength-dependentelectro-optic and/or electro-absorptive properties may be incorporatedinto the waveguide despite the lack of lattice compatibility of therequired materials.

[0231] Alternatively, the MLR stack(s) may be fabricated using materialsthat are lattice-compatible with the InGaAsP MQW system. A waveguide orresonator according to the present invention may include MLR stack(s)comprising alternating quarter-wave layers of InP (index of about 3.4)and aluminum oxide (index about 1.55 at 1.5 μm). The MLR stack depositedduring vertical fabrication (FIGS. 15-18 and 27-30) initially comprisesalternating layers of InP (quarter-wave thickness based on an index ofabout 3.4) and Al_(x)In_(1−x)As (quarter-wave thickness based on anindex of about 1.55), for example. The aluminum fraction may varybetween about 0.5 and about 1.0, preferably between about 0.8 and about1.0. AlAs/InAs super-lattice material (of substantially the same averagecomposition) may be employed instead of AlInAs. Lateral oxidation of thewaveguide results in substantially complete conversion of the AlInAslayers to aluminum oxide (as in FIGS. 44 and 46), thereby yielding a MLRstack comprising alternating quarter-wave layers of high-index InP andlow-index aluminum oxide. A waveguide core layer may preferably compriseInP, and doped InGaAs or InGaAsP may preferably be used for electricalcontact layers. Either p-type of n-type doping may be used for thecontact layers, and delta doping may be preferred. Buffer, cladding,and/or etch-stop layers, if present, may preferably comprise InP,InGaAs, or InGaAsP, and the waveguide may rest on an InP substrate.Other suitable materials may be equivalently employed for the substrateand/or the core, buffer, cladding, and/or etch-stop layers.

[0232] For a single-substrate vertical fabrication of a single- ordual-MLR device using InP/Al_(x)O_(y) MLR stack(s), a multi-quantum-wellmaterial comprising higher-bandgap InGaAsP barrier layers and lowerbandgap InGaAsP quantum well layers may be employed as theelectro-active material. This MQW material is lattice-compatible withthe InP/AlInAs MLR stack(s) initially deposited, thereby enablingsingle-substrate vertical fabrication. The wavelength range over whichthe useful electro-absorptive and/or electro-optic properties of thisMQW material may extend is from about 1.2 μm to about 1.7 μm, whichdetermines the possible design wavelengths for the waveguide and thecorresponding quarter-wave thicknesses for the MLR stack layers. The MQWmaterial may comprise the entire core layer (FIGS. 15-16 and 29-30), ormay comprise a separate layer (FIGS. 17-18 and 27-28). Waveguides ofthese compositions are further processed by lateral oxidation of theAlInAs layers, as shown in FIGS. 44 and 46, thereby producing a highindex contrast InP/Al_(x)O_(y) MLR stack (about 3.2 to about 1.5). Inthis and other cases where an entire quarter-wave layer is converted bylateral oxidation, the quarter-wave layer thickness for the initialmaterial deposited must be determined based on the index of the finalmaterial present after lateral processing (oxidation or otherwise).

[0233] For a single-substrate vertical fabrication of a single- ordual-MLR device using InP/Al_(x)O_(y) MLR stack(s), a multi-quantum-wellmaterial comprising higher-bandgap InGaAsP barrier layers and lowerbandgap InGaAsP quantum well layers may be employed as theelectro-active material in place of one or more layers of a MLR stack.This MQW material is lattice-compatible with the InP/AlInAs MLR stack(s)initially deposited, thereby enabling single-substrate verticalfabrication. The wavelength range over which the usefulelectro-absorptive and/or electro-optic properties of this MQW materialmay extend is from about 1.2 μm to about 1.7 μm, which determines thepossible design wavelengths for the waveguide and the correspondingquarter-wave thicknesses for the MLR stack layers. The MQW material maycomprise one or more layers of the MLR stack(s) (FIGS. 19-20 and 31-34).Waveguides of these compositions are further processed by lateraloxidation of the AlInAs layers (if present), as shown in FIGS. 44 and46, thereby producing a high index contrast InP/Al_(x)O_(y) MLR stack(about 3.2 to about 1.5). In this and other cases where an entirequarter-wave layer is converted by lateral oxidation, the quarter-wavelayer thickness for the initial material deposited must be determinedbased on the index of the final material present after lateralprocessing (oxidation or otherwise).

[0234] A waveguide or resonator according to the present invention mayinclude a MLR stack(s) comprising alternating quarter-wave layers ofAl_(x)In_(1−x)As (index of about 3.2) and Al_(y)O_(z) (index betweenabout 1.5 and 1.7). The MLR stack layers deposited during verticalfabrication (FIGS. 15-18 and 27-30) comprise alternating layers ofAl_(x)In_(1−x)As (quarter-wave thickness based on an index of about 3.2)and Al_(x′)In_(1−x′)As (quarter-wave thickness based on an index ofabout 1.6), with x<x′. The fraction x may range from about 0.8 to about0.9, while x′ may range between about 0.9 and about 1.0. Alternatively,AlAs/InAs super-lattice layers may be employed having relative AIAs andInAs sub-layer thicknesses yielding average Al/In fractions of x/1−x andx′/1−x′ for the initially deposited MLR layers. In either case (AlInAsor AlAs/InAs super-lattices), the aluminum fraction x of thelower-aluminum layers may vary with distance from the substrate,yielding a tapered waveguide structure. The electro-active layer maycomprise InGaAsP MQW materials as described hereinabove. Lateraloxidation of the waveguide proceeds more rapidly in theAl_(x′)In_(1−x)As MLR layers having the higher Al content. The lateraloxidation is allowed to proceed just to completion in theAl_(x′)In_(1−x′)As MLR layers, thereby leaving medial portions ofAl_(x)In_(1−x)As between lateral Al_(y)O_(z) portions in theAl_(x)In_(1−x)As layers (FIGS. 48 and 50). The resulting DBR stackcomprises low-index quarter-wave aluminum oxide layers alternating withlayers having a high-index quarter-wave Al_(x)In_(1−x)As medial portionsurrounded by low-index aluminum oxide lateral portions. In the instancewhere the Al_(x)In_(1−x)As medial portion comprises a super-latticematerial, the sub-layers are typically sufficiently thin that foroptical wavelengths typically used in the waveguides and resonators ofthe present invention, the optical mode behaves substantially as if thesuper-lattice layer were a uniform layer having an index equal to theaverage index of the sub-layers of the super-lattice. A core layer maypreferably comprise InGaAsP electro-active MQW material, and doped InP,InGaAs, or InGaAsP may preferably be used for electrical contact layers.Either p-type of n-type doping may be used for the contact layers, anddelta doping may be preferred. Buffer, cladding, and/or etch-stoplayers, if present, may preferably comprise InP, InGaAs, or InGaAsP, andthe waveguide may rest on an InP substrate. Other suitable materials maybe equivalently employed for the substrate and/or the core, buffer,cladding, and/or etch-stop layers.

[0235] The GaAs-compatible MQW materials discussed previously(GaAs/AlGaAs; GaAs/InGaAs; GaAs/InGaAsN) may be used with InP-compatibleMLR stack(s) using the multi-substrate vertical fabrication processes ofFIGS. 21-26 and 35-40 in similar manner to the use of InGaAsP MQW layerswith GaAs/AlGaAs MLR stack(s) described above.

[0236] A specific layer sequence is given in the table in the Appendixfor a dual-DBR waveguide structure for the 1.5 μm region. The waveguideis vertically fabricated according to the three-substrate scheme ofFIGS. 35 and 36 (electro-active core on InP) and horizontally fabricatedaccording to FIG. 41, 42, or 43 and FIG. 48 or 50. Layer composition andrefractive index is given for the layers as initially deposited andafter lateral oxidation. Quarter-wave thicknesses are determined basedon the layer index after oxidation. The DBR stacks comprise alternatingAlGaAs/Al_(x)O_(y) layers and the electro-active core layer comprisesInGaAsP MQW material. This specific structure is exemplary only, andshould not be construed as limiting the scope of inventive conceptsdisclosed and/or claimed herein.

[0237] Any and all specific material combinations and operatingwavelength ranges given here are exemplary, and should not be construedas limiting the scope of inventive concepts disclosed and/or claimedherein. In particular, as new material combinations and systems aredeveloped which facilitate enhanced material lattice compatibility andmore extensive operating wavelength ranges, such materials may beemployed in waveguides and resonators of the present invention whileremaining within the scope of inventive concepts disclosed and/orclaimed herein.

[0238] Waveguides and resonators according to the present invention mayfind wide applicability in the field of fiber-optic telecommunicationsand modulation and/or routing of optical signal power transmission. Suchresonators and waveguides may be readily incorporated into integratedoptical devices, and their unique optical properties enable operation atlower operating drive voltages than currently deployed devices, moreefficiently transfer of optical power to/from integrated opticaldevices, and/or lower insertion loss for optical devices. While thefollowing exemplary devices employ a fiber-optic tapertransverse-coupled to a multi-layer waveguide of the present invention,analogous devices may be equivalently implemented using other low-indextransmission optical waveguides transverse-coupled to the multi-layerwaveguide, including various fiber-optic waveguides, planar waveguidecircuit waveguides, and so forth.

[0239] An optical waveguide 5100 fabricated according to the presentinvention on substrate 5110 is shown in FIG. 51 transverse-coupled to atransmission optical waveguide, in this example fiber-optic taper 5190.The waveguide/taper assembly is shown as surface-transverse-coupled inthe exemplary embodiment of FIG. 51, but fiber taper 5190 mayequivalently be side-transverse-coupled to waveguide 5100, and theensuing discussion applies to either transverse-coupling geometry. Modalindex matching may be adjusted for substantially negligible transfer ofoptical signal between fiber taper 5190 and waveguide 5100, therebyallowing optical signal to be transmitted substantially undisturbedthrough fiber taper 5190 and/or waveguide 5100. Alternatively, modalindex matching may be adjusted for substantially complete transfer ofoptical signal between fiber taper 5190 and waveguide 5100. This simpleconfiguration may be employed to provide a variety of optical deviceshaving low insertion loss. For example, the device of FIG. 51 may serveas an input coupler for efficiently transferring optical signal powerfrom an optical fiber to an optical device integrated onto substrate5110. The efficient optical signal power transfer enabled bytransverse-coupling yields a device exhibiting low insertion loss. Thedevice of FIG. 51 may be similarly employed as an output coupler forefficiently transferring optical signal power from an optical deviceintegrated onto substrate 5110 to an optical fiber. Waveguide 5100 maybe designed and fabricated for passive modal index matching tofiber-taper 5190 or other transmission optical waveguide. Alternatively,waveguide 5100 may include one or more active layers for enabling activecontrol of modal-index matching and optical signal power transfer(yielding an input/output coupler that may be turned on/off in responseto an applied control signal).

[0240] If waveguide 5100 includes an active layer, then application of acontrol signal enables control of the modal index of a guided opticalmode of waveguide 5100, in turn enabling control of the relative modalindex matching condition between the optical mode of waveguide 5100 anda propagating optical mode of optical fiber taper 5190 and opticalsignal power transfer therebetween. An electronic control signal may beemployed, for example, applied to an electro-active layer throughcontact electrodes 5120 and 5130, the electrodes typically including ametal film to enable application of control signals to contact layers inthe multi-layer waveguide structure. The waveguide/taper assembly maytherefore be used for altering optical signal transmission through fibertaper 5190, for example, and would potentially require substantiallylower control voltage due to the highly dispersive MLR stack. A deviceas shown in FIG. 51 may be used as a variable optical attenuator (VOA),with the level of attenuation varying with the amount of optical signalpower transferred out of the optical fiber and into the waveguide (whichin turn depends on the modal-index-matching condition resulting from acontrol voltage applied to electrodes 5120/5130). If electrodes5120/5130 are adapted for receiving high-speed signals, device 5100 mayfunction as a non-resonant high-speed modulator for an optical signalcarried by fiber-optic taper 5190. The device of FIG. 51 may also beused as a 2×2 optical switch, enabling controlled transfer (or not, asdesired) of optical signals between waveguide 5100 and fiber-optic taper5190.

[0241] Waveguide 5100 may alternatively include an electro-absorptivelayer. Application of a control voltage through contact electrodes 5120and 5130 may enable control of optical loss in waveguide 5100, in turnenabling control of transmission of an optical signal throughfiber-optic taper 5190. Waveguide 5100 may alternatively include anon-linear-optical layer. Application of an optical signal may thereforeenable control of optical loss of waveguide 5100 and/ormodal-index-matching between waveguide 5100 and fiber-optic taper 5190,in turn enabling control of transmission of an optical signal throughfiber-optic taper 5190.

[0242] For this and subsequent embodiments of the present invention,some consideration of the size and placement of contact electrodes isrequired. For a surface-guiding and/or surface-coupled waveguide, anupper electrode (such as 5130) preferably does not extend across theentire width of the upper surface of the waveguide, but is confinedalong one or both sides of the waveguide upper surface so as to reduceelectrode-induced optical loss for the surface-guided optical mode. Anupper contact layer of the waveguide structure (which may generallyintroduce less optical loss than a metal film) may preferably extendacross substantially the entire width of the waveguide for applying thebias voltage thereto through electrical contact with the electrode. Fora non-surface-guiding and side-coupled waveguide, a contact electrodemay extend across the top surface of a waveguide. Similarly, a lowercontact electrode (such as 5120) preferably does not extend under thewaveguide, but provides electrical contact with a lower contact layer ofthe waveguide which does extend under the waveguide across substantiallythe entire width thereof. The length of the electrodes should preferablybe chosen to result in the desired degree of optical signal powertransfer according to the equations shown hereinabove.

[0243]FIG. 52 shows a simple Mach-Zender interferometer modulator 5200,similar to the prior-art device of FIG. 1, fabricated according to thepresent invention on a substrate 5210 and including an electro-opticlayer. The optical signal to be modulated may enter modulator 5200through entrance face 5202 (end-coupling) and divide into a fractionentering the two branches of modulator 5200. Application of controlvoltages through contact electrodes 5220/5222/5230/5232 enable controlof the relative modal indices of optical signal fractions propagatingthrough the two branches of modulator 5200, in turn enabling the controlthe relative phase of the optical signal fractions at exit face 5204.When the fractions constructively interfere at 5204, the transmission ofmodulator 5200 is substantially maximal (except for insertion loss).When the fractions destructively interfere at 5204, the transmission ofmodulator 5200 is minimal (preferably nearly zero). The highlydispersive properties of the DBR stack(s) of modulator 5200 result in asubstantially lower V_(π) for modulator 5200 (less than 1 volt;potentially less than about 100 mV) than for the lithium niobatemodulator of FIG. 1 (as much as 5 to 10 volts). A high-speed driver foramplifying high-speed electronic control signals is therefore not neededto control modulator 5200. Modulator 5200 may be a single- or dual-MLRdevice. Modulator 5200 may also include an electro-absorptive layer,thereby enabling control of optical loss. This may be useful forcontrolling overall transmission, or for balancing intensities in thetwo branches of the interferometer for modulation contrast enhancement.Alternatively, modulator 5200 may include a non-linear-optical layer forenabling control of relative phase and/or optical loss by application ofan optical control signal.

[0244] While the device of FIG. 52 requires lower high-speed controlvoltage, the optical signal to be modulated must still enter through endface 5202 and exit through end face 5204 (end-coupling), and modulator5200 therefore may exhibit relatively high insertion loss (as high asabout 12-15 dB; similar to the prior art device of FIG. 1). FIG. 53shows a Mach-Zender interferometer modulator 5300 fabricated accordingto the present invention as a waveguide structure on substrate 5310transverse-surface-coupled to a fiber-optic taper 5390 at an inputregion and an output region. The optical signal of fiber-taper 5390 maybe transferred to modulator 5300 by application of an input controlvoltage through contact electrodes 5320/5330 to impose the needed modalindex matching condition to achieve nearly complete transfer of opticalpower from fiber-taper 5390 to waveguide 5300. This input controlvoltage need not be modulated, and may therefore be adjusted to therequired level without the need for any high-speed driver. Once withinmodulator 5300, high-speed control voltages (or optical control signals)may be applied through contact electrodes 5322/5332/5324/5334 to controltransmission through modulator 5300 in a manner completely analogous tothat described hereinabove for modulator 5200. An output control voltage(which need not be modulated) applied through contact electrodes5326/5336 may be adjusted to achieve nearly complete transfer of anyoptical power transmitted through modulator 5300 back into fiber taper5390 in an output region of modulator 5300. This embodiment has thedesirable low V_(π) of the device of FIG. 52, but with extremely lowinsertion loss (less than about 3 dB, potentially even less than about 1dB). An optical detector integrated onto substrate 5310 at exit face5304 may serve as a useful diagnostic tool for monitoring theperformance of the device of FIG. 53. FIG. 54 shows a similarMach-Zender modulator waveguide 5300 side-transverse-coupled tofiber-optic waveguide 5390. If appropriately designed and sufficientlyaccurately fabricated, passive modal index matching may be employed atthe input and output regions, eliminating the need for electrodes5320/5330/5326/5336.

[0245]FIG. 58 illustrates an alternative Mach-Zender interferometeroptical modulator according to the present invention. This device may beused for controlled modulation of light transmission through a taperedoptical fiber. A fiber-optic taper 5890 is showntransversely-surface-coupled to a waveguide 5800 at separate input andoutput coupling regions 5805 and 5806, respectively. The modal index ofwaveguide 5800 and the lengths of the coupling regions 5805 and 5806 maybe designed so that about half of the optical power is transferred fromwaveguide 5800 to fiber-optic taper 5890 at each of the regions 5805 and5806 without application of any bias voltage (passivemodal-index-matching). Alternatively, an input bias voltage may beapplied to the input coupling region 5805 (active modal-index-matching)through contact electrodes 5820/5830, each typically comprising a metalfilm to enable application of a bias voltage to contact layers in themulti-layer waveguide structure. The applied bias voltage is chosen totransfer about half of the optical signal power between waveguide 5800and fiber-optic taper 5890. The output coupling region 5806 may besimilarly passive modal-index-matched or active modal-index-matched (bybiasing contact electrodes 5824/5834). When employed, input and outputbias voltages applied are typically not substantially altered once theappropriate voltage levels are determined for a desired degree oftransverse optical coupling, therefore no high-speed driver electronicsare required for the input or output bias.

[0246] The intermediate segments (between the coupling regions) of thefiber-optic taper 5890 and the waveguide 5800 may function respectivelyas the two arms of a Mach-Zender interferometer, through which twofraction of the optical signal propagate. Application of a modulatorcontrol voltage through contact electrodes 5822/5832 enables control ofthe modal index of the modulator fraction of the optical signal inwaveguide 5800 in the intermediate segment thereof. Control of the modalindex in turn enables control of the relative phase of the modulatorfraction and the fiber-optic taper fraction of the optical signal asthey reach the output coupling region. The relative phase may beadjusted to achieve substantially constructive interference of theoptical signal fractions in the fiber-optic taper (i.e., maximaltransmission through the tapered optical fiber), or alternatively toachieve substantially destructive interference of the optical signalfractions in the fiber-optic-taper (i.e., minimal transmission throughthe tapered optical fiber), thereby achieving the desired result ofcontrolled modulation of the overall transmission of optical powerthrough fiber-optic taper 5890.

[0247] The modulator control voltage may be varied between twooperational levels corresponding respectively to maximal transmission(constructive interference in the fiber-optic taper) and minimaltransmission (destructive interference in the fiber-optic taper). Thedifference between the operational voltage levels is V_(π), which may beless than one volt (and potentially even less) for the modulator of FIG.58 incorporating a dispersion-engineered multi-layer waveguide accordingto the present invention. The modulator may therefore be operatedwithout the need of a high voltage RF driver or amplifier, reducing thesize, expense, and power requirements of the modulator, and eliminatingbandwidth restrictions potentially imposed by a driver. The insertionloss of the device may be quite low (less than 3 dB, perhaps less than 1dB), particularly compared to the end-coupled device of FIG. 1. Thespatial-mode-matching requirements and resulting insertion losses of themodulator of FIG. 1 are not present in the modulator of FIG. 58. Anoptical detector integrated onto substrate 5810 at exit face 5804 ofwaveguide 5800 may serve as a useful diagnostic tool for monitoring theperformance of the device of FIG. 58. Alternatively, waveguide 5800 maybe optically coupled at its input end face 5802 and/or its output endface 5804 to other optical elements, including optical sources and/oroptical detectors, integrated onto substrate 5810.

[0248] While shown as substantially identical structures in the Figures,the input and output coupling regions of the Mach-Zender device need notbe symmetric. Whether biased (active) or passive, each coupling regionmay be specifically and separately configured depending on theoperational characteristics desired for a specific device. Byappropriately fabricating, configuring, controlling, biasing, and/oradjusting the input and/or output coupling regions, one or all of theaverage optical transmission level, transmission differential, thecontrast ratio, the power-off transmission state, and/or the power-ontransmission state of the modulator may be varied, for example.Equivalently, one may set desired minimum and maximum transmissionlevels for the modulator. Incorporation of an electro-absorptive layerin waveguide 5800 enables control of overall optical loss of themodulator. Optical control signals may be employed for control of awaveguide 5800 incorporating a non-linear-optical layer.

[0249] An alternative Mach-Zender interferometer optical modulatoraccording to the present invention is shown in FIG. 59. In this case afiber-optic taper 5990 is transversely-side-coupled to a waveguide 5900according to the present invention at input and output coupling regions5905 and 5906, respectively. Intermediate segments of waveguide 5900 andfiber-optic taper 5990 form respectively the two arms of a Mach-Zenderinterferometer. The modal index of waveguide 5900 and the lengths of thecoupling regions 5905 and 5906 may be designed so that about half of theoptical power is transferred between an optical mode of waveguide 5900and a propagating optical mode of fiber-optic taper 5990 at each of theregions 5905 and 5906 without application of any bias voltage (passivemodal index matching). Alternatively, an input bias voltage may beapplied via contact electrodes 5920/5930, and an output bias voltage maybe applied via contact electrodes 5924/5934, as described hereinabove(active modal index matching). A modulator control voltage may beapplied via contact electrodes 5922/5932. An optical detector integratedonto substrate 5910 at exit face 5904 of waveguide 5900 may serve as auseful diagnostic tool for monitoring the performance of the device ofFIG. 59. Alternatively, waveguide 5900 may be optically coupled at itsinput face 5902 and/or at its output face 5904 to other opticalelements, including optical sources and/or optical detectors, integratedonto substrate 5910. The operational characteristics and advantages,including low insertion loss and low V_(π), of the modulator of FIG. 59are similar to those of the modulator of FIG. 58.

[0250] Instead of operating as an electro-optic Mach-Zenderinterferometer modulator, the devices depicted in FIGS. 58 and 59 may beimplemented as electro-absorptive modulators. Waveguide 5800 or 5900 maybe fabricated with at least one electro-absorptive layer thereof. Theinput and output coupling regions (5805 and 5806, or 5905 and 5906) maybe biased or unbiased, and fabricated, configured, controlled, biased,and/or otherwise adjusted to provide substantially complete transfer ofoptical power between waveguide 5800 or 5900 and fiber-optic taper 5890or 5990, respectively. Application of a control voltage to theintermediate portion of waveguide 5800 or 5900 through electrodes5822/5832 or 5922/5932 may alter the optical transmission throughwaveguide 5800 or 5900 between substantially minimal and substantiallymaximal transmission. In this way the overall transmission throughfiber-optic taper 5890 or 5990 may be similarly modulated betweensubstantially minimal and substantially maximal transmission. Such anelectro-absorptive modulator has low insertion loss (less than about 3dB) and would require a drive voltage comparable to currentelectro-absorptive modulators. It may be desirable to provide theintermediate portion of fiber-optic taper 5890/5990 with a optical lossmechanism, so that any optical signal not transferred to waveguide5800/5900 is not transmitted through taper 5890/5990.

[0251] Instead of modulating optical transmission through a taperedoptical fiber, the devices of FIGS. 58 and 59 may be used instead tomodulate optical transmission from the waveguide to the optical fiber asin FIGS. 60 and 61. This may be particularly advantageous when a deviceof FIG. 60 or FIG. 61 is combined with an optical source (preferably adiode laser) integrated onto the same substrate as the waveguide andcoupled into the waveguide at an input end 5802 (FIG. 60) or 5902 (FIG.61). Control voltages applied to input and output coupling regions maybe employed to control the overall transmission of light from thewaveguide into the tapered optical fiber (active modal-index-matching),or passive modal-index-matching may be employed. Application ofhigh-speed control voltages to the intermediate region of the waveguideenables high-speed modulation of transmission of light from thewaveguide into the tapered optical fiber. When implemented with anintegrated optical source such as a diode laser, the devices of FIGS. 60and 61 each solve simultaneously the problems of: i) efficient couplingof light from the source into an optical fiber; and ii) high-speed, lowvoltage modulation of transmission of light from the source through thefiber.

[0252]FIG. 55 shows a simple 2×2 switch 5500, similar to the prior-artdevice of FIG. 2, fabricated according to the present invention on asubstrate 5510. The optical signal to be controlled may enter coupler5500 through entrance face 5502 or 5503 (end-coupled). Application ofcontrol voltages through contact electrodes 5520/5522/5530/5532 enablecontrol of the relative modal indices of coupler optical modespropagating through the coupling region of coupler 5500, in turnenabling the control the relative optical power reaching exit faces 5504and 5505. The highly dispersive properties of the MLR stack(s) ofcoupler 5500 result in a substantially lower V₀ for coupler 5500 (lessthan 1 volt; potentially less than about 100 mV) than for the lithiumniobate coupler of FIG. 2 (as much as 5 to 10 volts). A high-speeddriver for amplifying high-speed electronic control signals is thereforenot needed to control coupler 5500. Coupler 5500 may be a single- ordual-MLR device. Switch 5500 may also include an electro-absorptivelayer, thereby enabling control of optical loss. This may be useful forcontrolling overall transmission, or for balancing intensities in thetwo arm of the switch. Alternatively, switch 5500 may include anon-linear-optical layer for enabling control of relative phase and/oroptical loss by application of an optical control signal.

[0253] While the device of FIG. 55 requires lower high-speed controlvoltage, the optical signal to be controlled must still enter throughend faces 5502 or 5503 and exit through end faces 5504 and 5505, andswitch 5500 therefore exhibits relatively high insertion loss (as highas about 12-15 dB). FIG. 56 shows a 2×2 switch 5600 fabricated accordingto the present invention on substrate 5610, transverse-side-coupled to afirst fiber-optic taper 5690 at an input region and an output region,and transverse-surface-coupled to a second fiber-optic taper 5692 at aninput region and an output region. The optical signal from fiber-taper5690 or 5692 may be transferred to coupler 5600 by application of acontrol voltage through contact electrodes 5620/5630 or 5621/5631,respectively, to impose the needed index matching condition to achievenearly complete transfer of optical power from one of the fiber-tapers5690 or 5692 to coupler 5600. This input control voltage need not bemodulated, and may therefore be adjusted to the required level withoutthe need for any high-speed driver. Once within coupler 5600, high-speedcontrol voltages may be applied through contact electrodes5622/5632/5623/5633 to control transfer of optical power within coupler5600 in a manner completely analogous to that described hereinabove forcoupler 5500. Output control voltages applied through contact electrodes5624/5634 and 5625/5635 may be adjusted to achieve nearly completetransfer of any optical power transmitted through coupler 5600 back intofiber tapers 5690 and/or 5692 in output regions of coupler 5600. Thisembodiment has the desirable low V₀ of the device of FIG. 55, but withextremely low insertion loss (less than about 3 dB, potentially evenless than about 1 dB). Optical detectors integrated onto substrate 5610at exit faces 5604 and 5605 may serve as a useful diagnostic tool formonitoring the performance of the device of FIG. 56. Switch 5600 may befabricated as a transverse-side-coupled device or atransverse-surface-coupled device, and both possibilities illustrated inFIG. 56. Fiber-taper 5690 is shown side-coupled to switch 5600, whilefiber-taper 5692 is shown surface-coupled to switch 5600. The twoseparate waveguides of switch 5600 are shown transverse-side-coupled inFIG. 56. If appropriately designed and sufficiently accuratelyfabricated, passive modal index matching may be employed at the inputand output regions, eliminating the need for electrodes5620/5630/5621/5631/5624/5634/5625/5635.

[0254] The embodiment of FIG. 51 may be configured to function as a 2×2switch, with the fiber-optic taper 5190 and waveguide 5100 serving asthe two optical pathways of the switch. Application of a control voltageto electrodes 5120/5130 (or application of an optical control signal)alters the modal-index matching condition between taper 5190 andwaveguide 5100, so that entering optical signals either remain withinthe component through which they entered (taper 5190 or waveguide 5100),or are transferred to the other component. The dispersive MLR structureof the waveguide enables switching at low V₀.

[0255] A resonant optical power control device similar to thosedescribed in earlier-cited applications A13 and A22 is shown in FIG. 57.An optical resonator 5700 and a modulator waveguide 5702 are fabricatedaccording to the present invention as transverse-side-coupled structureson substrate 5710. A fiber-taper 5790 is shown transverse-side-coupledto resonator 5700. A specific wavelength component of an optical signalpropagating through fiber-taper 5690, resonant with a resonance ofresonator 5700, may transfer into resonator 5700. A desired level ofoptical power transfer may be achieved through application of a controlvoltage through contact electrodes 5720/5730 to control modal indexmatching between the fiber-taper 5790 and the resonator 5700.Alternatively, passive modal-index matching may be employed. Theresonance frequency of the resonator 5700 may be controlled byapplication of a control voltage through contact electrodes 5722/5732,by changing a modal index of resonant optical mode of resonator 5700. Alevel of optical loss for resonator 5700 may be controlled byapplication of a control voltage through contact electrodes 5724/5734,by changing modal index matching conditions between resonator 5700 andwaveguide 5702 and/or by changing optical absorption characteristics ofwaveguide 5702. Changing the level of optical loss of resonator 5700 inthis way in turn enables controlled modulation of transmission ofresonant optical signals through fiber-taper 5790. Such devices, theiroperation, and their fabrication are disclosed in greater detail inearlier-cited application A7. Resonator 5700 and/or modulator waveguide5702 may alternatively include a non-linear-optical layer for enablingcontrol of resonant frequency and/or optical loss by application of anoptical control signal.

[0256] The present invention has been set forth in the forms of itspreferred and alternative embodiments. It is nevertheless intended thatmodifications to the disclosed active optical waveguides and resonators,and methods of fabrication and use thereof, may be made withoutdeparting from inventive concepts disclosed and/or claimed herein.thickness composition before composition after (nm) lateral oxidationoxidation sub- n/a GaAs GaAs strate contact 100 n-delta doped InGaAsn-delta doped InGaAs buffer 500-1000 nm GaAs GaAs DBR 230Al_(0.98)Ga_(0.02)As Al_(x)O_(y) stack 130 Al_(0.94)Ga_(0.06)Asbilateral Al_(x)O_(y) medial Al_(0.94)Ga_(0.06)As 230Al_(0.98)Ga_(0.02)As Al_(x)O_(y) 130 Al_(0.94)Ga_(0.06)As bilateralAl_(x)O_(y) medial Al_(0.94)Ga_(0.06)As 230 Al_(0.98)Ga_(0.02)AsAl_(x)O_(y) 130 Al_(0.94)Ga_(0.06)As bilateral Al_(x)O_(y) medialAl_(0.94)Ga_(0.06)As 230 Al_(0.98)Ga_(0.02)As Al_(x)O_(y) 130Al_(0.94)Ga_(0.06)As bilateral Al_(x)O_(y) medial Al_(0.94)Ga_(0.06)As230 Al_(0.98)Ga_(0.02)As Al_(x)O_(y) 130 Al_(0.94)Ga_(0.06)As bilateralAl_(x)O_(y) medial Al_(0.94)Ga_(0.06)As 230 Al_(0.98)Ga_(0.02)AsAl_(x)O_(y) MQW 50 InGaAsP 1.2 μm InGaAsP EO core bandgap 1.2 μm bandgap9 InGaAsP 1.6 μm InGaAsP bandgap 1.6 μm bandgap 20 InGaAsP 1.2 μmInGaAsP bandgap 1.6 μm bandgap 9 InGaAsP 1.6 μm InGaAsP bandgap 1.6 μmbandgap 20 InGaAsP 1.2 μm InGaAsP bandgap 1.6 μm bandgap MQW 9 InGaAsP1.6 μm InGaAsP EO core bandgap 1.6 μm bandgap (con-) 20 InGaAsP 1.2 μmInGaAsP tinued bandgap 1.6 μm bandgap 9 InGaAsP 1.6 μm InGaAsP bandgap1.6 μm bandgap 20 InGaAsP 1.2 μm InGaAsP bandgap 1.6 μm bandgap 9InGaAsP 1.6 μm InGaAsP bandgap 1.6 μm bandgap 50 InGaAsP 1.2 μm InGaAsPbandgap 1.6 μm bandgap DBR 230 Al_(0.98)Ga_(0.02)As Al_(x)O_(y) stack130 Al_(0.94)Ga_(0.06)As bilateral Al_(x)O_(y) medialAl_(0.94)Ga_(0.06)As 230 Al_(0.98)Ga_(0.02)As Al_(x)O_(y) 130Al_(0.94)Ga_(0.06)As bilateral Al_(x)O_(y) medial Al_(0.94)Ga_(0.06)As230 Al_(0.98)Ga_(0.02)As Al_(x)O_(y) 130 Al_(0.94)Ga_(0.06)As bilateralAl_(x)O_(y) medial Al_(0.94)Ga_(0.06)As 230 Al_(0.98)Ga_(0.02)AsAl_(x)O_(y) 130 Al_(0.94)Ga_(0.06)As bilateral Al_(x)O_(y) medialAl_(0.94)Ga_(0.06)As 230 Al_(0.98)Ga_(0.02)As Al_(x)O_(y) 130Al_(0.94)Ga_(0.06)As bilateral Al_(x)O_(y) medial Al_(0.94)Ga_(0.06)As230 Al_(0.98)Ga_(0.02)As Al_(x)O_(y) contact 50 n-delta doped InGaAsn-delta doped InGaAs buffer/ 200 GaAs GaAs clad nm

What is claimed is:
 1. An optical device, comprising: a transmissionoptical waveguide; and an optical device component transverse-coupled tothe transmission optical waveguide so as to enable optical signal powertransfer therebetween, the transmission optical waveguide being adaptedfor at least one of receiving optical signal power from an opticalsignal transmission system and transmitting optical signal power to theoptical signal transmission system, the optical device componentincluding a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack, the optical device componentbeing transverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component.
 2. The opticaldevice of claim 1, the transmission optical waveguide being a low-indexoptical waveguide.
 3. The optical device of claim 2, the transmissionoptical waveguide being a fiber-optic transmission waveguide, thefiber-optic transmission waveguide being adapted for transverse-couplingwith the optical device component.
 4. The optical device of claim 3, thetransmission fiber-optic waveguide being adapted for at least one ofreceiving optical signal power form a fiber-optic telecommunicationssystem and transmitting optical signal power to a fiber-optictelecommunications system.
 5. An optical device, comprising: atransmission optical waveguide; and an optical device componenttransverse-coupled to the transmission optical waveguide so as to enableoptical signal power transfer therebetween, the transmission opticalwaveguide being adapted for at least one of receiving optical signalpower from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical device component including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack, theoptical device component being transverse-coupled to the transmissionoptical waveguide at the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for enablingmodal-index-matching between the transmission optical waveguide and theoptical device component, the transmission fiber-optic waveguideincluding a fiber-optic-taper segment, the fiber-optic-taper segmentbeing transverse-coupled to the optical device component.
 6. An opticaldevice, comprising: a transmission optical waveguide; and an opticaldevice component transverse-coupled to the transmission opticalwaveguide so as to enable optical signal power transfer therebetween,the transmission optical waveguide being adapted for at least one ofreceiving optical signal power from an optical signal transmissionsystem and transmitting optical signal power to the optical signaltransmission system, the optical device component including alaterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack, the optical device component beingtransverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the transmissionoptical waveguide being a low-index planar lightwave transmissionoptical waveguide.
 7. An optical device, comprising: a transmissionoptical waveguide; and an optical device component transverse-coupled tothe transmission optical waveguide so as to enable optical signal powertransfer therebetween, the transmission optical waveguide being adaptedfor at least one of receiving optical signal power from an opticalsignal transmission system and transmitting optical signal power to theoptical signal transmission system, the optical device componentincluding a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack, the optical device componentbeing transverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure being adapted for passive modal-index-matchingbetween the transmission optical waveguide and the multi-layer waveguidestructure.
 8. The optical device of claim 7, the multi-layer waveguidestructure including high-index material, the transmission opticalwaveguide being a low-index transmission optical waveguide.
 9. Anoptical device, comprising: a transmission optical waveguide; and anoptical device component transverse-coupled to the transmission opticalwaveguide so as to enable optical signal power transfer therebetween,the transmission optical waveguide being adapted for at least one ofreceiving optical signal power from an optical signal transmissionsystem and transmitting optical signal power to the optical signaltransmission system, the optical device component including alaterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack, the optical device component beingtransverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure being adapted for passive modal-index-matchingbetween the transmission optical waveguide and the multi-layer waveguidestructure, the multi-layer waveguide including high-index material, thetransmission optical waveguide being a transmission fiber-opticwaveguide including a fiber-optic-taper segment, the fiber-optic-tapersegment being transverse-coupled to the multi-layer waveguide structure.10. An optical device, comprising: a transmission optical waveguide; andan optical device component transverse-coupled to the transmissionoptical waveguide so as to enable optical signal power transfertherebetween, the transmission optical waveguide being adapted for atleast one of receiving optical signal power from an optical signaltransmission system and transmitting optical signal power to the opticalsignal transmission system, the optical device component including alaterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack, the optical device component beingtransverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure being adapted for passive modal-index-matchingbetween the transmission optical waveguide and the multi-layer waveguidestructure, the multi-layer waveguide structure including high-indexmaterial, the transmission optical waveguide being a low-index planarlightwave transmission optical waveguide.
 11. An optical device,comprising: a transmission optical waveguide; and an optical devicecomponent transverse-coupled to the transmission optical waveguide so asto enable optical signal power transfer therebetween, the transmissionoptical waveguide being adapted for at least one of receiving opticalsignal power from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical device component including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack, theoptical device component being transverse-coupled to the transmissionoptical waveguide at the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for enablingmodal-index-matching between the transmission optical waveguide and theoptical device component, the multi-layer waveguide structure beingadapted for passive modal-index-matching between the transmissionoptical waveguide and the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for integration into anintegrated optical device, the multi-layer waveguide structure beingadapted for substantially completely transferring optical signal powerbetween the transmission optical waveguide and the multi-layer waveguidestructure, the multi-layer waveguide structure being thereby adapted tofunction as at least one of a passive input coupler and a passive outputcoupler between the transmission optical waveguide and the integratedoptical device.
 12. An optical device, comprising: a transmissionoptical waveguide; and an optical device component transverse-coupled tothe transmission optical waveguide so as to enable optical signal powertransfer therebetween, the transmission optical waveguide being adaptedfor at least one of receiving optical signal power from an opticalsignal transmission system and transmitting optical signal power to theoptical signal transmission system, the optical device componentincluding a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack, the optical device componentbeing transverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure including an active layer, the active layerincluding at least one of an electro-active layer and anon-linear-optical layer, the multi-layer waveguide structure beingadapted so that varying a control signal applied to the active layerresults in at least one of varying optical loss and varying modal-indexfor the multi-layer waveguide structure.
 13. The optical device of claim12, the multi-layer waveguide structure including at least oneelectro-active layer, the electro-active layer including at least one ofan electro-optic layer and an electro-absorptive layer, the multi-layerwaveguide structure including a pair of electrical contact layers withthe electro-active layer therebetween, the control signal being anelectronic control signal applied through the electrical contact layers.14. The optical device of claim 12, the multi-layer waveguide structureincluding at least one non-linear-optical layer, the control signalbeing an optical control signal applied to the non-linear-optical layer.15. The optical device of claim 12, the multi-layer waveguide structureincluding high-index material, the transmission optical waveguide beinga low-index transmission optical waveguide, the multi-layer waveguidestructure being adapted for active modal-index-matching with thelow-index transmission optical waveguide in response to the controlsignal.
 16. An optical device, comprising: a transmission opticalwaveguide; and an optical device component transverse-coupled to thetransmission optical waveguide so as to enable optical signal powertransfer therebetween, the transmission optical waveguide being adaptedfor at least one of receiving optical signal power from an opticalsignal transmission system and transmitting optical signal power to theoptical signal transmission system, the optical device componentincluding a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack, the optical device componentbeing transverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure including an active layer, the active layerincluding at least one of an electro-active layer and anon-linear-optical layer, the multi-layer waveguide structure beingadapted so that varying a control signal applied to the active layerresults in at least one of varying optical loss and varying modal-indexfor the multi-layer waveguide structure, the multi-layer waveguideincluding high-index material, the transmission optical waveguide beinga transmission fiber-optic waveguide including a fiber-optic-tapersegment, the fiber-optic-taper segment being transverse-coupled to themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for active modal-index-matching with the fiber-optic-tapersegment in response to the control signal.
 17. An optical device,comprising: a transmission optical waveguide; and an optical devicecomponent transverse-coupled to the transmission optical waveguide so asto enable optical signal power transfer therebetween, the transmissionoptical waveguide being adapted for at least one of receiving opticalsignal power from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical device component including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack, theoptical device component being transverse-coupled to the transmissionoptical waveguide at the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for enablingmodal-index-matching between the transmission optical waveguide and theoptical device component, the multi-layer waveguide structure includingan active layer, the active layer including at least one of anelectro-active layer and a non-linear-optical layer, the multi-layerwaveguide structure being adapted so that varying a control signalapplied to the active layer results in at least one of varying opticalloss and varying modal-index for the multi-layer waveguide structure,the multi-layer waveguide structure including high-index material, thetransmission optical waveguide being a low-index planar lightwavetransmission optical waveguide, the multi-layer waveguide structurebeing adapted for active modal-index-matching with the low-index planarlightwave transmission optical waveguide in response to the controlsignal.
 18. An optical device, comprising: a transmission opticalwaveguide; and an optical device component transverse-coupled to thetransmission optical waveguide so as to enable optical signal powertransfer therebetween, the transmission optical waveguide being adaptedfor at least one of receiving optical signal power from an opticalsignal transmission system and transmitting optical signal power to theoptical signal transmission system, the optical device componentincluding a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack, the optical device componentbeing transverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure including an active layer, the active layerincluding at least one of an electro-active layer and anon-linear-optical layer, the multi-layer waveguide structure beingadapted so that varying a control signal applied to the active layerresults in at least one of varying optical loss and varying modal-indexfor the multi-layer waveguide structure, the multi-layer waveguidestructure being adapted for integration into an integrated opticaldevice, the multi-layer waveguide structure being adapted forsubstantially modal-index-matching with the transmission opticalwaveguide in response to the control signal so as to substantiallycompletely transfer optical signal power between the transmissionoptical waveguide and the multi-layer waveguide structure in response tothe control signal, the multi-layer waveguide structure being therebyadapted for functioning as at least one of an active input coupler andan active output coupler between the transmission optical waveguide andthe integrated optical device.
 19. An optical device, comprising: atransmission optical waveguide; and an optical device componenttransverse-coupled to the transmission optical waveguide so as to enableoptical signal power transfer therebetween, the transmission opticalwaveguide being adapted for at least one of receiving optical signalpower from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical device component including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack, theoptical device component being transverse-coupled to the transmissionoptical waveguide at the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for enablingmodal-index-matching between the transmission optical waveguide and theoptical device component, the multi-layer waveguide structure includingan active layer, the active layer including at least one of anelectro-active layer and a non-linear-optical layer, the multi-layerwaveguide structure being adapted so that varying a control signalapplied to the active layer results in at least one of varying opticalloss and varying modal-index for the multi-layer waveguide structure,the multi-layer waveguide structure being adapted for substantiallycompletely transferring optical signal power between the transmissionoptical waveguide and the multi-layer waveguide structure in response toa first control signal level, the multi-layer waveguide structure beingadapted for substantially preventing optical signal power transferbetween the transmission optical waveguide and the multi-layer waveguidestructure in response to a second control signal level, the opticaldevice being thereby adapted for functioning as an optical switch. 20.An optical device, comprising: a transmission optical waveguide; and anoptical device component transverse-coupled to the transmission opticalwaveguide so as to enable optical signal power transfer therebetween,the transmission optical waveguide being adapted for at least one ofreceiving optical signal power from an optical signal transmissionsystem and transmitting optical signal power to the optical signaltransmission system, the optical device component including alaterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack, the optical device component beingtransverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure including an active layer, the active layerincluding at least one of an electro-active layer and anon-linear-optical layer, the multi-layer waveguide structure beingadapted so that varying a control signal applied to the active layerresults in at least one of varying optical loss and varying modal-indexfor the multi-layer waveguide structure, the multi-layer waveguidestructure being adapted for allowing substantially maximal transmissionof optical signal power through the transmission optical waveguide inresponse to a first control signal level, the multi-layer waveguidestructure being adapted allowing substantially minimal transmission ofoptical signal power through the transmission optical waveguide inresponse to a second control signal level, the multi-layer waveguidestructure being adapted for allowing an intermediate transmission levelof optical signal power through the transmission optical waveguide inresponse to an intermediate control signal level, the optical devicebeing thereby adapted for functioning as at least one of an opticalmodulator and a variable optical attenuator.
 21. The optical device ofclaim 20, the multi-layer waveguide structure being adapted forexhibiting varying modal-index in response to varying control signallevel.
 22. The optical device of claim 20, the multi-layer waveguidestructure being adapted for exhibiting varying optical loss in responseto varying control signal level.
 23. An optical device, comprising: atransmission optical waveguide; and an optical device componenttransverse-coupled to the transmission optical waveguide so as to enableoptical signal power transfer therebetween, the transmission opticalwaveguide being adapted for at least one of receiving optical signalpower from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical device component including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack, theoptical device component being transverse-coupled to the transmissionoptical waveguide at the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for enablingmodal-index-matching between the transmission optical waveguide and theoptical device component, the multi-layer waveguide structure beingpositioned on a substrate, layers of the multi-layer waveguide structurebeing substantially parallel to the substrate.
 24. The optical device ofclaim 23, the multi-layer reflector stack comprising a distributed Braggreflector stack.
 25. The optical device of claim 23, the multi-layerwaveguide structure being fabricated at least in part by deposition oflayers on the substrate.
 26. The optical device of claim 23, themulti-layer waveguide structure including a single multi-layer reflectorstack, the multi-layer waveguide structure being thereby adapted forguiding a surface-guided optical mode.
 27. The optical device of claim23, the multi-layer waveguide structure including two multi-layerreflector stacks and a core layer therebetween, the multi-layerwaveguide structure being thereby adapted for guiding an optical modealong the core layer.
 28. An optical device, comprising: a transmissionoptical waveguide; and an optical device component transverse-coupled tothe transmission optical waveguide so as to enable optical signal powertransfer therebetween, the transmission optical waveguide being adaptedfor at least one of receiving optical signal power from an opticalsignal transmission system and transmitting optical signal power to theoptical signal transmission system, the optical device componentincluding a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack, the optical device componentbeing transverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure being positioned on a substrate, layers of themulti-layer waveguide structure being substantially parallel to thesubstrate, the multi-layer waveguide structure including a ridge-likewaveguide structure protruding from the substrate formed byspatially-selective removal of material of lateral portions of themulti-layer waveguide structure.
 29. The optical device of claim 28, thematerial being removed substantially completely down to the substrate.30. The optical device of claim 28, the material being only partiallyremoved.
 31. The optical device of claim 28, the material being removedsubstantially symmetrically from lateral portions of the multi-layerwaveguide structure.
 32. The optical device of claim 28, the materialbeing removed asymmetrically from lateral portions of the multi-layerwaveguide structure.
 33. The optical device of claim 28, thetransmission optical waveguide being transverse-coupled at a sidesurface of the multi-layer waveguide structure.
 34. The optical deviceof claim 28, the transmission optical waveguide being transverse-coupledat a top surface of the multi-layer waveguide structure.
 35. An opticaldevice, comprising: a transmission optical waveguide; and an opticaldevice component transverse-coupled to the transmission opticalwaveguide so as to enable optical signal power transfer therebetween,the transmission optical waveguide being adapted for at least one ofreceiving optical signal power from an optical signal transmissionsystem and transmitting optical signal power to the optical signaltransmission system, the optical device component including alaterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack, the optical device component beingtransverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure being positioned on a substrate, layers of themulti-layer waveguide structure being substantially parallel to thesubstrate, at least one layer of the multi-layer waveguide structurebeing provided with a lateral lower-index portion.
 36. The opticaldevice of claim 35, the lateral lower-index portion being provided ononly one side of the multi-layer waveguide structure.
 37. The opticaldevice of claim 35, the lateral lower-index portion being provided onboth sides of the multi-layer waveguide structure.
 38. The opticaldevice of claim 35, the lateral lower-index portion being provided byphysical modification of at least one lateral portion of at least onelayer.
 39. An optical device, comprising: a transmission opticalwaveguide; and an optical device component transverse-coupled to thetransmission optical waveguide so as to enable optical signal powertransfer therebetween, the transmission optical waveguide being adaptedfor at least one of receiving optical signal power from an opticalsignal transmission system and transmitting optical signal power to theoptical signal transmission system, the optical device componentincluding a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack, the optical device componentbeing transverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure being positioned on a substrate, layers of themulti-layer waveguide structure being substantially parallel to thesubstrate, at least one layer of the multi-layer waveguide structurebeing provided with a lateral lower-index portion, the laterallower-index portion being provided by deposition of lower-indexmaterial.
 40. An optical device, comprising: a transmission opticalwaveguide; and an optical device component transverse-coupled to thetransmission optical waveguide so as to enable optical signal powertransfer therebetween, the transmission optical waveguide being adaptedfor at least one of receiving optical signal power from an opticalsignal transmission system and transmitting optical signal power to theoptical signal transmission system, the optical device componentincluding a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack, the optical device componentbeing transverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure being positioned on a substrate, layers of themulti-layer waveguide structure being substantially parallel to thesubstrate, at least one layer of the multi-layer waveguide structurebeing provided with a lateral lower-index portion, the laterallower-index portion being provided by chemical modification of at leastone lateral portion of at least one layer.
 41. An optical device,comprising: a transmission optical waveguide; and an optical devicecomponent transverse-coupled to the transmission optical waveguide so asto enable optical signal power transfer therebetween, the transmissionoptical waveguide being adapted for at least one of receiving opticalsignal power from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical device component including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack, theoptical device component being transverse-coupled to the transmissionoptical waveguide at the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for enablingmodal-index-matching between the transmission optical waveguide and theoptical device component, the multi-layer waveguide structure beingpositioned on a substrate, layers of the multi-layer waveguide structurebeing substantially perpendicular to the substrate.
 42. The opticaldevice of claim 41, the multi-layer reflector stack comprising adistributed Bragg reflector stack.
 43. The optical device of claim 41,the multi-layer waveguide structure including two multi-layer reflectorstacks and a core layer therebetween, the multi-layer waveguidestructure being thereby adapted for guiding an optical mode along thecore layer.
 44. The optical device of claim 41, the multi-layerwaveguide structure being formed by spatially-selective processing ofwaveguide material deposited on the substrate.
 45. The optical device ofclaim 41, the transmission optical waveguide being transverse-coupled tothe multi-layer waveguide structure at a side surface thereof.
 46. Theoptical device of claim 41, the transmission optical waveguide beingtransverse-coupled to the multi-layer waveguide structure at a topsurface thereof.
 47. The optical device of claim 1, lateral confinementbeing provided by at least one lateral grating provided in at least onelayer.
 48. The optical device of claim 1, the multi-layer waveguidestructure including at least one dielectric multi-layer reflector stack.49. The optical device of claim 1, the multi-layer waveguide structureincluding at least one semi-conductor layer.
 50. The optical device ofclaim 49, the multi-layer waveguide structure including alternatinghigher-index GaAs and lower-index AlGaAs layers.
 51. The optical deviceof claim 50, at least one lower-index AlGaAs layer being provided withat least one lateral aluminum oxide portion.
 52. The optical device ofclaim 49, the multi-layer waveguide structure including alternatinghigher-index AlGaAs and lower-index aluminum oxide layers.
 53. Theoptical device of claim 52, at least one higher-index AlGaAs layer beingprovided with at least one lateral aluminum oxide portion.
 54. Theoptical device of claim 49, the multi-layer waveguide structureincluding alternating higher-index InP and lower-index IrAlAs layers.55. The optical device of claim 54, at least one lower-index InAlAslayer being provided with at least one lateral aluminum oxide portion.56. The optical device of claim 49, the multi-layer waveguide structureincluding alternating higher-index InAlAs and lower-index aluminum oxidelayers.
 57. The optical device of claim 56, at least one higher-indexlaAlAs layer being provided with at least one lateral aluminum oxideportion.
 58. The optical device of claim 49, the multi-layer waveguidestructure including alternating higher-index InP and lower-indexaluminum oxide layers.
 59. The optical device of claim 49, themulti-layer waveguide structure including alternating higher-index GaAsand lower-index aluminum oxide layers.
 60. An optical device,comprising: a transmission optical waveguide; and an optical devicecomponent transverse-coupled to the transmission optical waveguide so asto enable optical signal power transfer therebetween, the transmissionoptical waveguide being adapted for at least one of receiving opticalsignal power from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical device component including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack, theoptical device component being transverse-coupled to the transmissionoptical waveguide at the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for enablingmodal-index-matching between the transmission optical waveguide and theoptical device component, the multi-layer waveguide structure includingalternating higher-index semiconductor and lower-index semiconductorlayers.
 61. An optical device, comprising: a transmission opticalwaveguide; and an optical device component transverse-coupled to thetransmission optical waveguide so as to enable optical signal powertransfer therebetween, the transmission optical waveguide being adaptedfor at least one of receiving optical signal power from an opticalsignal transmission system and transmitting optical signal power to theoptical signal transmission system, the optical device componentincluding a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack, the optical device componentbeing transverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure including alternating higher-index semiconductor andlower-index semiconductor layers, at least one of the higher-indexsemiconductor layers and the lower-index semi-conductor layers beingprovided with at least one lateral oxidized portion.
 62. An opticaldevice, comprising: a transmission optical waveguide; and an opticaldevice component transverse-coupled to the transmission opticalwaveguide so as to enable optical signal power transfer therebetween,the transmission optical waveguide being adapted for at least one ofreceiving optical signal power from an optical signal transmissionsystem and transmitting optical signal power to the optical signaltransmission system, the optical device component including alaterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack, the optical device component beingtransverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure including alternating higher-index semiconductor andlower-index oxide layers.
 63. An optical device, comprising: atransmission optical waveguide; and an optical device componenttransverse-coupled to the transmission optical waveguide so as to enableoptical signal power transfer therebetween, the transmission opticalwaveguide being adapted for at least one of receiving optical signalpower from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical device component including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack, theoptical device component being transverse-coupled to the transmissionoptical waveguide at the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for enablingmodal-index-matching between the transmission optical waveguide and theoptical device component, the multi-layer waveguide structure includingalternating higher-index semiconductor and lower-index oxide layers, atleast one higher-index semiconductor layer being provided with at leastone lateral oxidized portion.
 64. An optical device, comprising: atransmission optical waveguide; and an optical device componenttransverse-coupled to the transmission optical waveguide so as to enableoptical signal power transfer therebetween, the transmission opticalwaveguide being adapted for at least one of receiving optical signalpower from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical device component including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack, theoptical device component being transverse-coupled to the transmissionoptical waveguide at the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for enablingmodal-index-matching between the transmission optical waveguide and theoptical device component, at least one layer of the multi-layerwaveguide structure including an aluminum-containing semiconductor. 65.An optical device, comprising: a transmission optical waveguide; and anoptical device component transverse-coupled to the transmission opticalwaveguide so as to enable optical signal power transfer therebetween,the transmission optical waveguide being adapted for at least one ofreceiving optical signal power from an optical signal transmissionsystem and transmitting optical signal power to the optical signaltransmission system, the optical device component including alaterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack, the optical device component beingtransverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, at least one layerof the multi-layer waveguide structure being provided with at least onelateral aluminum oxide portion.
 66. An optical device, comprising: atransmission optical waveguide; and an optical device componenttransverse-coupled to the transmission optical waveguide so as to enableoptical signal power transfer therebetween, the transmission opticalwaveguide being adapted for at least one of receiving optical signalpower from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical device component including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack, theoptical device component being transverse-coupled to the transmissionoptical waveguide at the multi-layer waveguide structure, themulti-layer waveguide structure being adapted for enablingmodal-index-matching between the transmission optical waveguide and theoptical device component, the multi-layer waveguide structure includingat least one semiconductor active layer.
 67. The optical device of claim66, at least one semiconductor active layer being lattice-compatiblewith the multi-layer reflector stack.
 68. The optical device of claim66, at least one semiconductor active layer being lattice-incompatiblewith the multi-layer reflector stack.
 69. The optical device of claim66, at least one semiconductor active layer being an InGaAs layer. 70.The optical device of claim 66, at least one semiconductor active layerbeing an InGaAsP layer.
 71. The optical device of claim 66, at least onesemiconductor active layer being an InGaAsN layer.
 72. An opticaldevice, comprising: a transmission optical waveguide; and an opticaldevice component transverse-coupled to the transmission opticalwaveguide so as to enable optical signal power transfer therebetween,the transmission optical waveguide being adapted for at least one ofreceiving optical signal power from an optical signal transmissionsystem and transmitting optical signal power to the optical signaltransmission system, the optical device component including alaterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack, the optical device component beingtransverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure including at least one semiconductor active layer,at least one semiconductor active layer being an electro-absorptivelayer.
 73. An optical device, comprising: a transmission opticalwaveguide; and an optical device component transverse-coupled to thetransmission optical waveguide so as to enable optical signal powertransfer therebetween, the transmission optical waveguide being adaptedfor at least one of receiving optical signal power from an opticalsignal transmission system and transmitting optical signal power to theoptical signal transmission system, the optical device componentincluding a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack, the optical device componentbeing transverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure including at least one semiconductor active layer,at least one semiconductor active layer being an electro-optic layer.74. An optical device, comprising: a transmission optical waveguide; andan optical device component transverse-coupled to the transmissionoptical waveguide so as to enable optical signal power transfertherebetween, the transmission optical waveguide being adapted for atleast one of receiving optical signal power from an optical signaltransmission system and transmitting optical signal power to the opticalsignal transmission system, the optical device component including alaterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack, the optical device component beingtransverse-coupled to the transmission optical waveguide at themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling modal-index-matching between the transmissionoptical waveguide and the optical device component, the multi-layerwaveguide structure including at least one semiconductor active layer,at least one semiconductor layer being a non-linear-optic layer.
 75. Anoptical modulator, comprising: an input optical waveguide; an outputoptical waveguide; a first intermediate optical waveguide connecting theinput and output optical waveguides; and a second intermediate opticalwaveguide connecting the input and output optical waveguides, the inputoptical waveguide being adapted for receiving optical signal power froman optical signal transmission system, for dividing the received opticalsignal power into first and second optical signal power fractions, andfor transmitting the first and second optical signal power fractions tothe first and second intermediate optical waveguides, respectively, theoutput optical waveguide being adapted for receiving and recombining thefirst and second optical signal power fractions from the first andsecond intermediate optical waveguides, respectively, the output opticalwaveguide being adapted for substantially maximally transmitting therecombined optical signal power to the optical transmission system whenthe recombined first and second optical signal fractions substantiallyconstructively interfere, and for substantially minimally transmittingthe recombined optical signal power to the optical transmission systemwhen the recombined first and second optical signal fractionssubstantially destructively interfere, the input waveguide, outputwaveguide, first intermediate waveguide, and second intermediatewaveguide each comprising a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack and atleast one active layer, the active layer being adapted for exhibiting atleast one of varying optical loss and varying modal-index in response toan applied control signal, at least one of the first and secondintermediate waveguides being adapted for receiving the control signal,the multi-layer waveguide structure being adapted so that varying thecontrol signal applied to at least one of the first and secondintermediate waveguides results in a varying modal-index, therebyenabling control of interference between the recombined first and secondoptical signal power fractions at the output waveguide.
 76. An opticalmodulator, comprising: an input optical waveguide; an output opticalwaveguide; a first intermediate optical waveguide connecting the inputand output optical waveguides; and a second intermediate opticalwaveguide connecting the input and output optical waveguides, the inputwaveguide, output waveguide, first intermediate waveguide, and secondintermediate waveguide each including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack and atleast one active layer, the active layer being adapted for exhibiting atleast one of varying optical loss and varying modal-index in response toa varying applied control signal, at least one of the first and secondintermediate waveguides being adapted for receiving the control signal,the input optical waveguide being adapted for receiving optical signalpower from an optical signal transmission system, for dividing thereceived optical signal power into first and second optical signal powerfractions, and for transmitting the first and second optical signalpower fractions to the first and second intermediate optical waveguides,respectively, the output optical waveguide being adapted for receivingand recombining the first and second optical signal power fractions fromthe first and second intermediate optical waveguides, respectively, andtransmitting the recombined fractions to the optical signal transmissionsystem, the optical modulator being thereby adapted so that varying thecontrol signal level results in a varying level of transmission of therecombined fractions to the optical signal transmission system.
 77. Theoptical modulator of claim 76, the active layer including at least oneelectro-active layer, the electro-active layer including at least one ofan electro-optic layer and an electro-absorptive layer, at least one ofthe intermediate waveguides including a pair of electrical contacts withthe electro-active layer therebetween, the control signal being anelectrical control signal applied through the electrical contacts. 78.The optical modulator of claim 76, the active layer including at leastone non-linear optical layer, the control signal being an opticalcontrol signal applied to a portion of the non-linear-optical layer inat least one of the intermediate waveguides.
 79. The optical modulatorof claim 76, the multi-layer waveguide structure including a singlemulti-layer waveguide stack, the multi-layer waveguide structure beingthereby adapted for guiding a surface-guided optical mode.
 80. Theoptical modulator of claim 76, the multi-layer waveguide structureincluding two multi-layer reflector stacks and a core layertherebetween, the multi-layer waveguide structure being thereby adaptedfor guiding an optical mode along the core layer.
 81. The opticalmodulator of claim 76, the input optical waveguide being adapted forreceiving optical signal power from the optical signal transmissionsystem by end-coupling, the output optical waveguide being adapted fortransmitting optical signal power to the optical signal transmissionsystem by end-coupling.
 82. An optical modulator, comprising: an inputoptical waveguide; an output optical waveguide; a first intermediateoptical waveguide connecting the input and output optical waveguides;and a second intermediate optical waveguide connecting the input andoutput optical waveguides, the input waveguide, output waveguide, firstintermediate waveguide, and second intermediate waveguide each includinga laterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack and at least one active layer, the activelayer being adapted for exhibiting at least one of varying optical lossand varying modal-index in response to a varying applied control signal,at least one of the first and second intermediate waveguides beingadapted for receiving the control signal, the input optical waveguidebeing adapted for receiving optical signal power from an optical signaltransmission system, for dividing the received optical signal power intofirst and second optical signal power fractions, and for transmittingthe first and second optical signal power fractions to the first andsecond intermediate optical waveguides, respectively, the output opticalwaveguide being adapted for receiving and recombining the first andsecond optical signal power fractions from the first and secondintermediate optical waveguides, respectively, and transmitting therecombined fractions to the optical signal transmission system, theoptical modulator being thereby adapted so that varying the controlsignal level results in a varying level of transmission of therecombined fractions to the optical signal transmission system, theinput optical waveguide being adapted for receiving optical signal powerfrom the optical signal transmission system by transverse-coupling to atransmission optical waveguide, the output optical waveguide beingadapted for transmitting optical signal power to the optical signaltransmission system by transverse-coupling to a transmission opticalwaveguide.
 83. The optical modulator of claim 82, the multi-layerwaveguide structure including a high-index material.
 84. The opticalmodulator of claim 82, the transmission optical waveguide being alow-index transmission optical waveguide, the low-index waveguide beingadapted for transverse-coupling.
 85. The optical modulator of claim 82,the transmission optical waveguide being a transmission fiber-opticwaveguide, the transmission fiber-optic waveguide being adapted fortransverse-coupling.
 86. An optical modulator, comprising: an inputoptical waveguide; an output optical waveguide; a first intermediateoptical waveguide connecting the input and output optical waveguides;and a second intermediate optical waveguide connecting the input andoutput optical waveguides, the input waveguide, output waveguide, firstintermediate waveguide, and second intermediate waveguide each includinga laterally-confined multi-layer dispersion-engineered waveguidestructure, the multi-layer waveguide structure including at least onemulti-layer reflector stack and at least one active layer, the activelayer being adapted for exhibiting at least one of varying optical lossand varying modal-index in response to a varying applied control signal,at least one of the first and second intermediate waveguides beingadapted for receiving the control signal, the input optical waveguidebeing adapted for receiving optical signal power from an optical signaltransmission system, for dividing the received optical signal power intofirst and second optical signal power fractions, and for transmittingthe first and second optical signal power fractions to the first andsecond intermediate optical waveguides, respectively, the output opticalwaveguide being adapted for receiving and recombining the first andsecond optical signal power fractions from the first and secondintermediate optical waveguides, respectively, and transmitting therecombined fractions to the optical signal transmission system, theoptical modulator being thereby adapted so that varying the controlsignal level results in a varying level of transmission of therecombined fractions to the optical signal transmission system, theinput optical waveguide being adapted for receiving optical signal powerfrom the optical signal transmission system by transverse-coupling to atransmission optical waveguide, the output optical waveguide beingadapted for transmitting optical signal power to the optical signaltransmission system by transverse-coupling to a transmission opticalwaveguide, the transmission optical waveguide being a transmissionfiber-optic waveguide including a fiber-optic-taper segment, thefiber-optic-taper segment being adapted for transverse-coupling.
 87. Anoptical modulator, comprising: an input optical waveguide; an outputoptical waveguide; a first intermediate optical waveguide connecting theinput and output optical waveguides; and a second intermediate opticalwaveguide connecting the input and output optical waveguides, the inputwaveguide, output waveguide, first intermediate waveguide, and secondintermediate waveguide each including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack and atleast one active layer, the active layer being adapted for exhibiting atleast one of varying optical loss and varying modal-index in response toa varying applied control signal, at least one of the first and secondintermediate waveguides being adapted for receiving the control signal,the input optical waveguide being adapted for receiving optical signalpower from an optical signal transmission system, for dividing thereceived optical signal power into first and second optical signal powerfractions, and for transmitting the first and second optical signalpower fractions to the first and second intermediate optical waveguides,respectively, the output optical waveguide being adapted for receivingand recombining the first and second optical signal power fractions fromthe first and second intermediate optical waveguides, respectively, andtransmitting the recombined fractions to the optical signal transmissionsystem, the optical modulator being thereby adapted so that varying thecontrol signal level results in a varying level of transmission of therecombined fractions to the optical signal transmission system, theinput optical waveguide being adapted for receiving optical signal powerfrom the optical signal transmission system by transverse-coupling to atransmission optical waveguide, the output optical waveguide beingadapted for transmitting optical signal power to the optical signaltransmission system by transverse-coupling to a transmission opticalwaveguide, the transmission optical waveguide being a low-index planarlightwave transmission optical waveguide, the planar lightwavetransmission optical waveguide being adapted for transverse-coupling.88. An optical modulator, comprising: a transmission optical waveguide,the transmission optical waveguide including a first transverse-couplingsegment, an intermediate segment, and a second transverse-couplingsegment; and a modulator optical waveguide, the modulator opticalwaveguide including a first transverse-coupling segment, an intermediatesegment, and a second transverse-coupling segment, the transmissionoptical waveguide and the modulator optical waveguide beingtransverse-coupled at the respective first transverse-coupling segmentsthereof, the transmission optical waveguide and the modulator opticalwaveguide being transverse-coupled at the respective secondtransverse-coupling segments thereof, the transmission optical waveguidebeing adapted for receiving optical signal power from an optical signaltransmission system into the first transverse-coupling segment thereof,the first transverse-coupling segment of the transmission opticalwaveguide and the first transverse-coupling segment of the modulatoroptical waveguide being adapted for dividing, via transverse opticalcoupling therebetween, the received optical signal power into amodulator waveguide fraction and a transmission waveguide fraction, andfor transmitting the fractions to the respective intermediate waveguidesegments, the second transverse-coupling segment of the transmissionoptical waveguide and the second transverse-coupling segment of themodulator optical waveguide being adapted for receiving and recombining,via transverse optical coupling, the modulator waveguide fraction andthe transmission waveguide fraction, the second transverse-couplingsegment of the transmission optical waveguide and the secondtransverse-coupling segment of the modulator optical waveguide beingadapted for substantially maximally transmitting the recombined opticalsignal power to the optical signal transmission system when therecombined modulator waveguide fraction and transmission waveguidefraction substantially constructively interfere in the transmissionoptical waveguide, and for substantially minimally transmitting therecombined optical signal power to the optical signal transmissionsystem when the recombined modulator waveguide fraction and transmissionwaveguide fraction substantially destructively interfere in thetransmission optical waveguide, the modulator optical waveguidecomprising a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer structure including at least onemulti-layer reflector stack and at least one active layer, the activelayer being adapted for exhibiting at least one of varying optical lossand varying modal-index in response to an applied control signal, themulti-layer waveguide structure being adapted so that varying thecontrol signal applied to the intermediate waveguide segment results ina varying modal-index, thereby enabling control of interference betweenthe recombined modulator waveguide fraction and transmission waveguidefraction in the transmission optical waveguide.
 89. An opticalmodulator, comprising: a transmission optical waveguide, thetransmission optical waveguide including a first transverse-couplingsegment, an intermediate segment, and a second transverse-couplingsegment; and a modulator optical waveguide, the modulator opticalwaveguide including a first transverse-coupling segment, an intermediatesegment, and a second transverse-coupling segment, the transmissionoptical waveguide and the modulator optical waveguide beingtransverse-coupled at the respective first transverse-coupling segmentsthereof, the transmission optical waveguide and the modulator opticalwaveguide being transverse-coupled at the respective secondtransverse-coupling segments thereof, the transmission optical waveguidebeing adapted for receiving optical signal power from an optical signaltransmission system into the first transverse-coupling segment thereof,the modulator optical waveguide comprising a laterally-confinedmulti-layer dispersion-engineered waveguide structure, the multi-layerstructure including at least one multi-layer reflector stack and atleast one active layer, the active layer being adapted for exhibiting atleast one of varying optical loss and varying modal-index in response toan applied control signal, the first transverse-coupling segment of thetransmission optical waveguide and the first transverse-coupling segmentof the modulator optical waveguide being adapted for dividing, viatransverse optical coupling therebetween, the received optical signalpower into a modulator waveguide fraction and a transmission waveguidefraction, and for transmitting the fractions to the respectiveintermediate waveguide segments, the second transverse-coupling segmentof the transmission optical waveguide and the second transverse-couplingsegment of the modulator optical waveguide being adapted for receiving,and recombining via transverse optical coupling the modulator waveguidefraction and the transmission waveguide fraction, and transmitting therecombined fractions to the optical signal transmission system, themulti-layer waveguide structure being adapted so that varying thecontrol signal applied to the intermediate waveguide segment results ina varying level of transmission of the recombined fractions to theoptical signal transmission system.
 90. The optical modulator of claim89, the active layer including at least one electro-active layer, theelectro-active layer including at least one of an electro-optic layerand an electro-absorptive layer, the intermediate segment of themodulator optical waveguide including a pair of electrical contacts withthe electro-active layer therebetween, the control signal being anelectrical control signal applied through the electrical contacts. 91.The optical modulator of claim 89, the active layer including at leastone non-linear optical layer, the control signal being an opticalcontrol signal applied to a portion of the non-linear-optical layer inthe intermediate segment of the modulator optical waveguide.
 92. Theoptical modulator of claim 89, the multi-layer waveguide structureincluding a single multi-layer waveguide stack, the multi-layerwaveguide structure being thereby adapted for guiding a surface-guidedoptical mode.
 93. The optical modulator of claim 89, the multi-layerwaveguide structure including two multi-layer reflector stacks and acore layer therebetween, the multi-layer waveguide structure beingthereby adapted for guiding an optical mode along the core layer. 94.The optical modulator of claim 89, the first transverse-coupling segmentof the transmission optical waveguide and the first transverse-couplingsegment of the modulator optical waveguide being passively substantiallymodal-index-matched, the second transverse-coupling segment of thetransmission optical waveguide and the second transverse-couplingsegment of the modulator optical waveguide being passively substantiallymodal-index-matched.
 95. The optical modulator of claim 89, the firsttransverse-coupling segment of the transmission optical waveguide andthe first transverse-coupling segment of the modulator optical waveguidebeing actively substantially modal-index-matched by applying an inputcontrol signal to the active layer in the first transverse-couplingsegment of the modulator optical waveguide, the secondtransverse-coupling segment of the transmission optical waveguide andthe second transverse-coupling segment of the modulator opticalwaveguide being actively substantially modal-index-matched by applyingan output control signal to the active layer in the secondtransverse-coupling segment of the modulator optical waveguide.
 96. Theoptical modulator of claim 89, the multi-layer waveguide structureincluding a high-index material.
 97. The optical modulator of claim 89,the transmission optical waveguide being a low-index transmissionoptical waveguide, the low-index waveguide being adapted fortransverse-coupling.
 98. The optical modulator of claim 89, thetransmission optical waveguide being a transmission fiber-opticwaveguide, the transmission fiber-optic waveguide being adapted fortransverse-coupling.
 99. An optical modulator, comprising: atransmission optical waveguide, the transmission optical waveguideincluding a first transverse-coupling segment, an intermediate segment,and a second transverse-coupling segment; and a modulator opticalwaveguide, the modulator optical waveguide including a firsttransverse-coupling segment, an intermediate segment, and a secondtransverse-coupling segment, the transmission optical waveguide and themodulator optical waveguide being transverse-coupled at the respectivefirst transverse-coupling segments thereof, the transmission opticalwaveguide and the modulator optical waveguide being transverse-coupledat the respective second transverse-coupling segments thereof, thetransmission optical waveguide being adapted for receiving opticalsignal power from an optical signal transmission system into the firsttransverse-coupling segment thereof, the modulator optical waveguidecomprising a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer structure including at least onemulti-layer reflector stack and at least one active layer, the activelayer being adapted for exhibiting at least one of varying optical lossand varying modal-index in response to an applied control signal, thefirst transverse-coupling segment of the transmission optical waveguideand the first transverse-coupling segment of the modulator opticalwaveguide being adapted for dividing, via transverse optical couplingtherebetween, the received optical signal power into a modulatorwaveguide fraction and a transmission waveguide fraction, and fortransmitting the fractions to the respective intermediate waveguidesegments, the second transverse-coupling segment of the transmissionoptical waveguide and the second transverse-coupling segment of themodulator optical waveguide being adapted for receiving, and recombiningvia transverse optical coupling the modulator waveguide fraction and thetransmission waveguide fraction, and transmitting the recombinedfractions to the optical signal transmission system, the multi-layerwaveguide structure being adapted so that varying the control signalapplied to the intermediate waveguide segment results in a varying levelof transmission of the recombined fractions to the optical signaltransmission system, the transmission optical waveguide being atransmission fiber-optic waveguide including a fiber-optic-tapersegment, the fiber-optic-taper segment being adapted fortransverse-coupling.
 100. An optical modulator, comprising: atransmission optical waveguide, the transmission optical waveguideincluding a first transverse-coupling segment, an intermediate segment,and a second transverse-coupling segment; and a modulator opticalwaveguide, the modulator optical waveguide including a firsttransverse-coupling segment, an intermediate segment, and a secondtransverse-coupling segment, the transmission optical waveguide and themodulator optical waveguide being transverse-coupled at the respectivefirst transverse-coupling segments thereof, the transmission opticalwaveguide and the modulator optical waveguide being transverse-coupledat the respective second transverse-coupling segments thereof, thetransmission optical waveguide being adapted for receiving opticalsignal power from an optical signal transmission system into the firsttransverse-coupling segment thereof, the modulator optical waveguidecomprising a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer structure including at least onemulti-layer reflector stack and at least one active layer, the activelayer being adapted for exhibiting at least one of varying optical lossand varying modal-index in response to an applied control signal, thefirst transverse-coupling segment of the transmission optical waveguideand the first transverse-coupling segment of the modulator opticalwaveguide being adapted for dividing, via transverse optical couplingtherebetween, the received optical signal power into a modulatorwaveguide fraction and a transmission waveguide fraction, and fortransmitting the fractions to the respective intermediate waveguidesegments, the second transverse-coupling segment of the transmissionoptical waveguide and the second transverse-coupling segment of themodulator optical waveguide being adapted for receiving, and recombiningvia transverse optical coupling the modulator waveguide fraction and thetransmission waveguide fraction, and transmitting the recombinedfractions to the optical signal transmission system, the multi-layerwaveguide structure being adapted so that varying the control signalapplied to the intermediate waveguide segment results in a varying levelof transmission of the recombined fractions to the optical signaltransmission system, the transmission optical waveguide being alow-index planar lightwave transmission optical waveguide, the planarlightwave transmission optical waveguide being adapted fortransverse-coupling.
 101. An optical switch, comprising: a first opticalwaveguide, the first optical waveguide including an input segment, atransverse-coupling segment, and an output segment; and a second opticalwaveguide, the second optical waveguide including an input segment, atransverse-coupling segment, and an output segment, the first and secondoptical waveguides being transverse-coupled at the respectivetransverse-coupling segments thereof, the input segments of the firstand second optical waveguides each being adapted for receiving opticalsignal power from an optical signal transmission system and transmittingreceived optical signal power to the respective transverse-couplingsegment, the output segments of the first and second optical waveguideseach being adapted for receiving optical signal power from therespective transverse-coupling segments and transmitting the opticalsignal power to the optical signal transmission system, the first andsecond optical waveguides each comprising a laterally-confinedmulti-layer dispersion-engineered waveguide structure, the multi-layerwaveguide structure including at least one multi-layer reflector stackand at least one active layer, the active layer being adapted forexhibiting at least one of varying optical loss and varying modal-indexin response to an applied control signal, the multi-layer waveguidestructure being adapted so that varying the control signal applied to atleast one of the transverse-coupling segments results in optical signalpower transfer between the first and second transmission opticalwaveguides.
 102. The optical switch of claim 101, the active layerincluding at least one electro-active layer, the electro-active layerincluding at least one of an electro-optic layer and anelectro-absorptive layer, the transverse coupling segment of at leastone of the optical waveguides including a pair of electrical contactswith the electro-active layer therebetween, the control signal being anelectrical control signal applied through the electrical contacts. 103.The optical switch of claim 101, the active layer including at least onenon-linear optical layer, the control signal being an optical controlsignal applied to a portion of the non-linear-optical layer in thetransverse-coupling segment of at least one of the optical waveguides.104. The optical switch of claim 101, the multi-layer waveguidestructure including a single multi-layer waveguide stack, themulti-layer waveguide structure being thereby adapted for guiding asurface-guided optical mode.
 105. The optical switch of claim 101, themulti-layer waveguide structure including two multi-layer reflectorstacks and a core layer therebetween, the multi-layer waveguidestructure being thereby adapted for guiding an optical mode along thecore layer.
 106. The optical switch of claim 101, the input segments ofthe first and second optical waveguides being adapted for receivingoptical signal power from the optical signal transmission system byend-coupling, the output segments of the first and second opticalwaveguides being adapted for transmitting optical signal power to theoptical signal transmission system by end-coupling.
 107. An opticalswitch, comprising: a first optical waveguide, the first opticalwaveguide including an input segment, a transverse-coupling segment, andan output segment; and a second optical waveguide, the second opticalwaveguide including an input segment, a transverse-coupling segment, andan output segment, the first and second optical waveguides beingtransverse-coupled at the respective transverse-coupling segmentsthereof, the input segments of the first and second optical waveguideseach being adapted for receiving optical signal power from an opticalsignal transmission system and transmitting received optical signalpower to the respective transverse-coupling segment, the output segmentsof the first and second optical waveguides each being adapted forreceiving optical signal power from the respective transverse-couplingsegments and transmitting the optical signal power to the optical signaltransmission system, the first and second optical waveguides eachcomprising a laterally-confined multi-layer dispersion-engineeredwaveguide structure, the multi-layer waveguide structure including atleast one multi-layer reflector stack and at least one active layer, theactive layer being adapted for exhibiting at least one of varyingoptical loss and varying modal-index in response to an applied controlsignal, the multi-layer waveguide structure being adapted so thatvarying the control signal applied to at least one of thetransverse-coupling segments results in optical signal power transferbetween the first and second transmission optical waveguides, the inputsegments of the first and second optical waveguides being adapted forreceiving optical signal power from the optical signal transmissionsystem by transverse-coupling to a transmission optical waveguide, theoutput segments of the first and second optical waveguides being adaptedfor transmitting optical signal power to the optical signal transmissionsystem by transverse coupling to a transmission optical waveguide. 108.The optical switch of claim 107, the multi-layer waveguide structureincluding a high-index material.
 109. The optical switch of claim 107,the transmission optical waveguide being a low-index transmissionoptical waveguide, the low-index waveguide being adapted fortransverse-coupling.
 110. The optical switch of claim 107, thetransmission optical waveguide being a transmission fiber-opticwaveguide, the transmission fiber-optic waveguide being adapted fortransverse-coupling.
 111. An optical switch, comprising: a first opticalwaveguide, the first optical waveguide including an input segment, atransverse-coupling segment, and an output segment; and a second opticalwaveguide, the second optical waveguide including an input segment, atransverse-coupling segment, and an output segment, the first and secondoptical waveguides being transverse-coupled at the respectivetransverse-coupling segments thereof, the input segments of the firstand second optical waveguides each being adapted for receiving opticalsignal power from an optical signal transmission system and transmittingreceived optical signal power to the respective transverse-couplingsegment, the output segments of the first and second optical waveguideseach being adapted for receiving optical signal power from therespective transverse-coupling segments and transmitting the opticalsignal power to the optical signal transmission system, the first andsecond optical waveguides each comprising a laterally-confinedmulti-layer dispersion-engineered waveguide structure, the multi-layerwaveguide structure including at least one multi-layer reflector stackand at least one active layer, the active layer being adapted forexhibiting at least one of varying optical loss and varying modal-indexin response to an applied control signal, the multi-layer waveguidestructure being adapted so that varying the control signal applied to atleast one of the transverse-coupling segments results in optical signalpower transfer between the first and second transmission opticalwaveguides, the input segments of the first and second opticalwaveguides being adapted for receiving optical signal power from theoptical signal transmission system by transverse-coupling to atransmission optical waveguide, the output segments of the first andsecond optical waveguides being adapted for transmitting optical signalpower to the optical signal transmission system by transverse couplingto a transmission optical waveguide, the transmission optical waveguidebeing a transmission fiber-optic waveguide including a fiber-optic-tapersegment, the fiber-optic-taper segment being adapted fortransverse-coupling.
 112. An optical switch, comprising: a first opticalwaveguide, the first optical waveguide including an input segment, atransverse-coupling segment, and an output segment; and a second opticalwaveguide, the second optical waveguide including an input segment, atransverse-coupling segment, and an output segment, the first and secondoptical waveguides being transverse-coupled at the respectivetransverse-coupling segments thereof, the input segments of the firstand second optical waveguides each being adapted for receiving opticalsignal power from an optical signal transmission system and transmittingreceived optical signal power to the respective transverse-couplingsegment, the output segments of the first and second optical waveguideseach being adapted for receiving optical signal power from therespective transverse-coupling segments and transmitting the opticalsignal power to the optical signal transmission system, the first andsecond optical waveguides each comprising a laterally-confinedmulti-layer dispersion-engineered waveguide structure, the multi-layerwaveguide structure including at least one multi-layer reflector stackand at least one active layer, the active layer being adapted forexhibiting at least one of varying optical loss and varying modal-indexin response to an applied control signal, the multi-layer waveguidestructure being adapted so that varying the control signal applied to atleast one of the transverse-coupling segments results in optical signalpower transfer between the first and second transmission opticalwaveguides, the input segments of the first and second opticalwaveguides being adapted for receiving optical signal power from theoptical signal transmission system by transverse-coupling to atransmission optical waveguide, the output segments of the first andsecond optical waveguides being adapted for transmitting optical signalpower to the optical signal transmission system by transverse couplingto a transmission optical waveguide, the transmission optical waveguidebeing a low-index planar lightwave transmission optical waveguide, theplanar lightwave transmission optical waveguide being adapted fortransverse-coupling.
 113. A resonant optical device, comprising: atransmission optical waveguide; and an optical resonatortransverse-coupled to the transmission optical waveguide so as to enableoptical signal power transfer therebetween, the transmission opticalwaveguide being adapted for at least one of receiving optical signalpower from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical resonator including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack and atleast one active layer, the active layer being adapted for exhibiting atleast one of varying optical loss and varying modal-index in response toan applied control signal, the optical resonator beingtransverse-coupled to the transmission optical waveguide through themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling control, by application of a control signal,of at least one of optical signal power transfer between thetransmission optical waveguide and the optical resonator, a resonantfrequency of the optical resonator, and optical loss of the opticalresonator, thereby further enabling modulation of transmission ofoptical signal power through the transmission optical waveguide when theoptical signal is substantially resonant with the optical resonator.114. The optical modulator of claim 113, the active layer including atleast one electro-active layer, the electro-active layer including atleast one of an electro-optic layer and an electro-absorptive layer, theoptical resonator including a pair of electrical contacts with at leasta portion of the electro-active layer therebetween, the control signalbeing an electrical control signal applied through the electricalcontacts.
 115. The optical modulator of claim 113, the active layerincluding at least one non-linear optical layer, the control signalbeing an optical control signal applied to the non-linear-optical layerin at least a portion of the optical resonator.
 116. The opticalmodulator of claim 113, the multi-layer waveguide structure including asingle multi-layer waveguide stack, the multi-layer waveguide structurebeing thereby adapted for guiding a surface-guided optical mode. 117.The optical modulator of claim 113, the multi-layer waveguide structureincluding two multi-layer reflector stacks and a core layertherebetween, the multi-layer waveguide structure being thereby adaptedfor guiding an optical mode along the core layer.
 118. The opticalmodulator of claim 113, the optical resonator and the transmissionoptical waveguide being passively substantially modal-index-matched atrespective transverse-coupling segments thereof.
 119. The opticalmodulator of claim 113, the optical resonator and the transmissionoptical waveguide being actively substantially modal-index-matched atrespective transverse-coupling segments thereof by applying a controlsignal to the active layer in the transverse-coupling segment of theoptical resonator.
 120. The optical modulator of claim 113, themulti-layer waveguide structure including a high-index material. 121.The optical modulator of claim 113, the transmission optical waveguidebeing a low-index transmission optical waveguide, the low-indexwaveguide being adapted for transverse-coupling.
 122. The opticalmodulator of claim 113, the transmission optical waveguide being atransmission fiber-optic waveguide, the transmission fiber-opticwaveguide being adapted for transverse-coupling.
 123. A resonant opticaldevice, comprising: a transmission optical waveguide; and opticalresonator transverse-coupled to the transmission optical waveguide so asto enable optical signal power transfer therebetween, the transmissionoptical waveguide being adapted for at least one of receiving opticalsignal power from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical resonator including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack and atleast one active layer, the active layer being adapted for exhibiting atleast one of varying optical loss and varying modal-index in response toan applied control signal, the optical resonator beingtransverse-coupled to the transmission optical waveguide through themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling control, by application of a control signal,of at least one of optical signal power transfer between thetransmission optical waveguide and the optical resonator, a resonantfrequency of the optical resonator, and optical loss of the opticalresonator, thereby further enabling modulation of transmission ofoptical signal power through the transmission optical waveguide when theoptical signal is substantially resonant with the optical resonator, thetransmission optical waveguide being a transmission fiber-opticwaveguide including a fiber-optic-taper segment, the fiber-optic-tapersegment being adapted for transverse-coupling.
 124. A resonant opticaldevice, comprising: a transmission optical waveguide; and an opticalresonator transverse-coupled to the transmission optical waveguide so asto enable optical signal power transfer therebetween, the transmissionoptical waveguide being adapted for at least one of receiving opticalsignal power from an optical signal transmission system and transmittingoptical signal power to the optical signal transmission system, theoptical resonator including a laterally-confined multi-layerdispersion-engineered waveguide structure, the multi-layer waveguidestructure including at least one multi-layer reflector stack and atleast one active layer, the active layer being adapted for exhibiting atleast one of varying optical loss and varying modal-index in response toan applied control signal, the optical resonator beingtransverse-coupled to the transmission optical waveguide through themulti-layer waveguide structure, the multi-layer waveguide structurebeing adapted for enabling control, by application of a control signal,of at least one of optical signal power transfer between thetransmission optical waveguide and the optical resonator, a resonantfrequency of the optical resonator, and optical loss of the opticalresonator, thereby further enabling modulation of transmission ofoptical signal power through the transmission optical waveguide when theoptical signal is substantially resonant with the optical resonator, thetransmission optical waveguide being a low-index planar lightwavetransmission optical waveguide, the planar lightwave transmissionoptical waveguide being adapted for transverse-coupling.
 125. A methodfor fabricating a multi-layer laterally-confined dispersion-engineeredoptical waveguide structure, comprising the steps of: depositing a layerstructure on a substrate, the layer structure including a multi-layerreflector stack and an active layer; and spatially-selectivelyprocessing at least a portion of at least one of the multi-layerreflector stack and the active layer so as to provide lateralconfinement for a guided optical mode.
 126. The method of claim 125,farther including the step of processing at least one side of themulti-layer waveguide structure to provide at least one layer of themulti-layer waveguide structure with at least one lateral lower-indexportion.
 127. A method for fabricating a multi-layer laterally-confineddispersion-engineered optical waveguide structure, comprising the stepsof: depositing a layer structure on a substrate, the layer structureincluding a multi-layer reflector stack and an active layer;spatially-selectively processing at least a portion of at least one ofthe multi-layer reflector stack and the active layer so as to providelateral confinement for a guided optical mode; and processing at leastone side of the multi-layer waveguide structure to provide at least onelayer of the multi-layer waveguide structure with at least one laterallower-index portion, the lateral lower-index portion being provided byoxidation of a lateral portion of the layer.
 128. A method forfabricating a multi-layer laterally-confined dispersion-engineeredoptical waveguide structure, comprising the steps of: depositing a firstlayer structure on a first substrate, the first layer structureincluding a multi-layer reflector stack; depositing a second layerstructure on a second substrate, the second layer structure including anactive layer; securedly positioning the second substrate relative to thefirst substrate so as to substantially eliminate voids between the firstand second layer structures; removing the second substrate while leavingthe at least a portion of the second layer structure; andspatially-selectively processing at least a portion of at least one ofthe first and second layer structures so as to provide lateralconfinement for a guided optical mode.
 129. The method of claim 128,further including the step of processing at least one side of themulti-layer waveguide structure to provide at least one layer thereofwith at least one lateral lower-index portion thereof.
 130. A method forfabricating a multi-layer laterally-confined dispersion-engineeredoptical waveguide structure, comprising the steps of: depositing a firstlayer structure on a first substrate, the first layer structureincluding a multi-layer reflector stack; depositing a second layerstructure on a second substrate, the second layer structure including anactive layer; securedly positioning the second substrate relative to thefirst substrate so as to substantially eliminate voids between the firstand second layer structures; removing the second substrate while leavingthe at least a portion of the second layer structure;spatially-selectively processing at least a portion of at least one ofthe first and second layer structures so as to provide lateralconfinement for a guided optical mode; and processing at least one sideof the multi-layer waveguide structure to provide at least one layerthereof with at least one lateral lower-index portion thereof, thelateral lower-index portion being provided by oxidation of a portion ofthe layer.
 131. A method for fabricating a multi-layerlaterally-confined dispersion-engineered optical waveguide structure,comprising the steps of: depositing a layer structure on a substrate,the layer structure including a first multi-layer reflector stack, asecond multi-layer reflector stack, a core layer therebetween, and anactive layer; and spatially-selectively processing at least one of thefirst and second multi-layer-reflector stacks, the core layer, and theactive layer, thereby providing lateral confinement for a guided opticalmode.
 132. The method of claim 131, further including the step ofprocessing at least one side of the multi-layer waveguide structure toprovide at least one layer thereof with at least one lateral lower-indexportion thereof.
 133. A method for fabricating a multi-layerlaterally-confined dispersion-engineered optical waveguide structure,comprising the steps of: depositing a layer structure on a substrate,the layer structure including a first multi-layer reflector stack, asecond multi-layer reflector stack, a core layer therebetween, and anactive layer; spatially-selectively processing at least one of the firstand second multi-layer-reflector stacks, the core layer, and the activelayer, thereby providing lateral confinement for a guided optical mode;and processing at least one side of the multi-layer waveguide structureto provide at least one layer thereof with at least one laterallower-index portion thereof, the lateral lower-index portion beingprovided by oxidation of a portion of the layer.
 134. A method forfabricating a multi-layer laterally-confined dispersion-engineeredoptical waveguide structure, comprising the steps of: depositing a firstlayer structure on a first substrate, the first layer structureincluding a first multi-layer reflector stack; depositing a second layerstructure on a second substrate, the second layer structure including asecond multi-layer reflector stack, at least one of the first and secondlayer structures including a core layer, at least one of the first andsecond layer structures including an active layer; securedly positioningthe second substrate relative to the first substrate so as tosubstantially eliminate voids between the first and second layerstructures and so as to position the core layer between the first andsecond multi-layer reflector stacks; removing one of the first andsecond substrates while leaving at least a portion of each of the firstmulti-layer reflector stack, the core, the second multi-layer reflectorstack, and the active layer; and spatially-selectively processing atleast one of the first multi-layer reflector stack, the core layer, thesecond multi-layer reflector stack, and the active layer, therebyproviding lateral confinement for a guided optical mode.
 135. The methodof claim 134, further including the step of processing at least one sideof the multi-layer waveguide structure to provide at least one layerthereof with at least one lateral lower-index portion thereof.
 136. Amethod for fabricating a multi-layer laterally-confineddispersion-engineered optical waveguide structure, comprising the stepsof: depositing a first layer structure on a first substrate, the firstlayer structure including a first multi-layer reflector stack;depositing a second layer structure on a second substrate, the secondlayer structure including a second multi-layer reflector stack, at leastone of the first and second layer structures including a core layer, atleast one of the first and second layer structures including an activelayer; securedly positioning the second substrate relative to the firstsubstrate so as to substantially eliminate voids between the first andsecond layer structures and so as to position the core layer between thefirst and second multi-layer reflector stacks; removing one of the firstand second substrates while leaving at least a portion of each of thefirst multi-layer reflector stack, the core, the second multi-layerreflector stack, and the active layer; spatially-selectively processingat least one of the first multi-layer reflector stack, the core layer,the second multi-layer reflector stack, and the active layer, therebyproviding lateral confinement for a guided optical mode; and processingat least one side of the multi-layer waveguide structure to provide atleast one layer thereof with at least one lateral lower-index portionthereof, the lateral lower-index portion being provided by oxidation ofa portion of the layer.
 137. A method for fabricating a multi-layerlaterally-confined dispersion-engineered optical waveguide structure ona substrate, comprising the steps of: depositing a first layer structureon a first substrate, the first layer structure including a firstmulti-layer reflector stack; depositing a second layer structure on asecond substrate, the second layer structure including a secondmulti-layer reflector stack; depositing third layer structure on a thirdsubstrate, the third layer structure including an active layer, at leastone of the first, second, and third layer structures including a corelayer; securedly positioning the third substrate relative to the firstsubstrate so as to substantially eliminate voids between the first andthird layer structures; removing the third substrate while leaving atleast a portion of the active layer; securedly positioning the secondsubstrate relative to the first substrate so as to substantiallyeliminate voids between the second and third layer structures and so asto position the core layer between the first and second multi-layerreflector stacks; removing the second substrate while leaving at least aportion of the second multi-layer reflector stack; andspatially-selectively processing at least one of the first multi-layerreflector stack, the core layer, the second multi-layer reflector stack,and the active layer, thereby providing lateral confinement for a guidedoptical mode.
 138. The method of claim 137, further including the stepof processing at least one side of the multi-layer waveguide structureto provide at least one layer thereof with at least one laterallower-index portion thereof.
 139. A method for fabricating a multi-layerlaterally-confined dispersion-engineered optical waveguide structure ona substrate, comprising the steps of: depositing a first layer structureon a first substrate, the first layer structure including a firstmulti-layer reflector stack; depositing a second layer structure on asecond substrate, the second layer structure including a secondmulti-layer reflector stack; depositing third layer structure on a thirdsubstrate, the third layer structure including an active layer, at leastone of the first, second, and third layer structures including a corelayer; securedly positioning the third substrate relative to the firstsubstrate so as to substantially eliminate voids between the first andthird layer structures; removing the third substrate while leaving atleast a portion of the active layer; securedly positioning the secondsubstrate relative to the first substrate so as to substantiallyeliminate voids between the second and third layer structures and so asto position the core layer between the first and second multi-layerreflector stacks; removing the second substrate while leaving at least aportion of the second multi-layer reflector stack; spatially-selectivelyprocessing at least one of the first multi-layer reflector stack, thecore layer, the second multi-layer reflector stack, and the activelayer, thereby providing lateral confinement for a guided optical mode;and processing at least one side of the multi-layer waveguide structureto provide at least one layer thereof with at least one laterallower-index portion thereof, the lateral lower-index portion beingprovided by oxidation of a portion of the layer.